A very simple form of "reduplication" builds a new word or phrase by repeating a given word or phrase. An example of such a pattern is the word "tom tom". This is a very primitive human impulse that begins with baby talk. Words like these are sometimes called "tautonyms".
A couple minor points arise in listing these creatures.
First, it's sometimes hard to know whether a particular word is properly spelled with a hyphen, a space, or as a run on word. Thus, all three spellings "blah-blah", "blah blah" and "blahblah" might look reasonable, and might all turn up in written discourse. There are few clear rules on what to do here.
When the repeated word ends with a "y" sound, it may be spelled just as often with an "ie" ending as with "y". Certainly "goody goody" looks right and "goodie goodie" does not, but other cases are difficult to judge.
When listing these words alphabetically, it sometimes seems more natural to list by just the first half; but this rule conflicts with rigid dictionary order, and that can cause grief.
aa (rough lava stone) ack ack (anti-aircraft fire) agal-agal (agar-agar) agar-agar (a kind of seaweed used in gelatinous soups) aiaiai (Greek mythological nymphs who inhabited the island of Aiaia) Aku Aku angang-angang (a Javanese gong) antinganting (a Philippine charm or amulet) aye-aye (a sailor's assent; a lemur) Ayo-Ayo (a town in Bolivia) ba ba (a sponge cake) Baden Baden (a spa resort in Germany) Bali Bali bandy-bandy (a nocturnal Australian snake) barabara (a hut made from sod, used in northern Siberia) BB (a small round bullet used in children's guns) beebee (a small round bullet used in children's guns) bellabella (an Indian tribe of the central coast of British Columbia) Berber (an indigenous people of northwest Africa) beri beri (a nutritional disease) Bibi (a name) bibi (?) Bio Bio (a river in Chile) blah blah (pointless talk) blemblem (occurs in the "Circe" section of Ulysses, and as best we can tell, is a German slang word for "crazy") bling-bling (showy jewelry) bo-bo (marijuana) bolo bolo (a West African tree) bonbon (a candy) booboo (a mistake; an minor injury) boing boing (a tourist) boola boola (a college cheer) boomboom (a gun; the sound of falling) Bora Bora (a South Pacific island) boubou (crack cocaine) bou bou (a traditional long shapeless West African garment) bouncy bouncy (sexual intercourse) broom-broom (a car) bubu (a traditional long shapeless West African garment) buckety-buckety (cheap; inferior) buddy buddy (friendly) Budge Budge (a town in India) budli-budli (sodomy) bufu-bufu (fat, swollen) buibui (the black head-to-toe covering worn by Zanzibar women) bulbul (a Persian nightingale) bullen-bullen (the lyre bird) bunga-bunga (how Italian premier Silvio Berlusconi described his sex parties) [the] Bungle Bungle range (an Australian mountain range) bunyan-bunyan (an Australian evergreen timber tree) bye bye (farewell) caca (excrement) cadang-cadang (a blight affecting coconut trees) can can (a dance) cass-cass (untidy, disreputable) cha cha (a dance) chaka-chaka (messy; disorderly) [to] chang-chang (to cut hair in an amateurish way) che-che (a poor white) chee-chee (mincing English, elaborate idiom; a derogatory term for a Eurasian) chichi (very fashionable) chimachima (a South American hawk) chin chin (a drinking toast; casual chat) chinachina (the quinine tree) chip chip (farewell) chiquichiqui (a South American palm) chocho (a language spoken in Mexico, also known as Chocholtec) choo choo (baby talk for a locomotive) chop chop (quickly, without delay) chow chow (a Chinese dog; a hodgepodge, hash or stew) Coco (a name) coco (a palm tree) cocoa (an extract of the cacao bean, from which chocolate is made) couscous (a type of food) [to] cow-cow (to scold) coxcox (a legendary Mexican counterpart of Noah) craw craw (a parasitic skin disease of the inner thighs) cuckoo (a bird with a crazy laugh) cuscus (a Malay arboreal phalanger; the grain of African millet, the fibrous root of an Indian grass) cush-cush (a South American starch plant, relative of the yam) cuss-cuss (a quarrel) dab dab (a stoker's name for sailors, who are always painting) Dada (an art movement) dada (a child's name for father) daily daily (an anti-malarial pill that must be taken daily) dap-dap (a well-dressed attractive person) daw-daw (stupid) day-day ("goodbye") Deedee (a name) dege-dege (little, skimpy) deuce deuce (a 22 caliber pistol) dibbi-dibbi (an insignificant thing or person) dig-dig (a village in the Philippines) dik-dik (a small African antelope) dindin (baby talk for "dinner") ding-ding (a street car) [the] Dirty Dirty (the South) dividivi (the curved pods of a small tropical American tree, used for tanning and dyeing) Dob-Dob (a member of a Tibetan monk military order) dodo (a flightless, stupid, extinct bird; a person who should be extinct) Dol Dol (a town in Kenya) doo doo (baby talk for "excrement") doublet doublet (a printer's term for material that is accidentally printed printed twice) drip-drip (a repetitive dripping sound) Drodro (a village in the Congo) dub-dub (w/w, that is, a waiter/waitress) dub dub dub (a shortened form of the "WWW" that is part of a World Wide Web address) duk-duk (a secret society of the Tolai people of the Rabaul area of new Britain) dumdum (a stupid person; a nasty bullet) Duran Duran (a character in "Barbarella"; a flashy hair band) dust dust (a newly promoted corporal or sergeant) [The] Ex Ex (The United States Exploring Expedition, 1838-1842) eye eye (an expression meaning "look at that!") faux-faux (an imitation of an imitation shearling coat) fen-phen (a combination of "herbal" weight loss drugs that killed people, without destroying the reputation of health food stores and "nutritional supplement" vendors) fenky-fenky (cowardly) Fia Fia (a Samoan festival of dancing and singing) fie fie (a person of bad character) Fifi (a name) fifty fifty (a fair division into two parts; even odds) flaba-flaba (worthless) floy floy (venereal disease; pizzazz) foo-foo (a fool; an outsider) footie-footie (footsie) four-four (a common musical time signature) froufrou (the sound of silk rustling; excessive ornamentation) fukfuk (animal innards) furfur (dandruff) gabble gabble (idle talk) gado-gado (a Singapore dish of a cooked vegetable salad, hardboiled egg, and peanut sauce) gaga (infatuated; demented) galang-galang (the Australian locust) galgal (a barrow) gang gang (an Australian cockatoo) geegee (an inferior race horse) Gigi (a name) gillie gilly (a boy, young man, or manservant in the Scottish Highlands) girly-girly (effeminate) goody goody (an expression of delight; an overly proper person) gogo (enthusiastic; lively) googoo (an imitation of baby talk) goo goo (a person who emphasizes the possibilities of good government) greng-greng (coarse short hair) grigri (a magical charm used to send bad luck to a rival) grisgris (an African charm) Grong Grong (a town in Australia) gru-gru (a spiny tropical palm related to the coconut palm) gugu (?) guid-guid (a small brightly colored tropical bird, the honey creeper) guit-guit (a small brightly colored tropical bird, the honey creeper) gully-gully (Arab street performers) Gumly Gumly (a town in Australia) gupgup (gossip) ha ha (an imitation of the sound of laughter) harry harry (rum) haw haw (an imitation of the sound of laughter) hee hee (an imitation of the sound of laughter) he he (an imitation of the sound of laughter) heh heh (an imitation of the sound of laughter) Hibhib (a town in Iraq) high-high (?) ho ho (an exclamation made upon discovery) ho ho ho (how Santa Claus frightens children) housie housie (the British name for bingo) housey housey (the British name for bingo) hubba hubba (a cry of enthusiasm) huet-huet (a small brightly colored tropical bird, the honey creeper) huhu (a very large beetle of New Zealand) Hui-Hui (a Chinese Muslim) hula-hula (a traditional Hawaiian dance) hum-hum (a rough Indian cotton fabric) hush hush (secret) ieie (a Hawaiian screwpine) ilang ilang (a tree) Iloilo (a port town and province of Panay island in the Philippines) ipilipil (a Philippine shrub) itai itai (cadmium poisoning disease, from the Japanese for "ouch, ouch!") jappa jappa (rough, indifferent) jeng-jeng (something worthless) jigjig (sexual intercourse) Jojo (a name) juju (a drug in a capsule; a magical amulet) kaba-kaba (a low, worthless person) kabu kabu (a Nigerian motorcycle taxi) kai-kai (?) kak-kak (a small heron or bittern of Guam) kaka (excrement) kass kass (an argument) kavakava (the drug or "dietary supplement" kava) kawakawa (a New Zealand shrub) Kerrikerri (an African tribe) Khoi-Khoi (a tribe of South Africa and Namibia) kho-kho (an Indian game of tag, using two teams of 12 people) khus-khus (vetiver, a kind of grass) kie-kie (a New Zealand climbing plant) killeekillee kiwikiwi (the kiwi bird) klop-klop (?) knock knock (imitation of the sound of knocking) knockie knockie (sexual intercourse) Koko (a name) koko (?) kookoo (a catchall disease in Ghana) Kou Kou (a town in Chad) kuku (?) kukukuku (a small, aggressive tribe of New Guinea) kumkum (a red powder used in India to mark the forehead) kuskus (?) lala (?) La La [land] (Los Angeles; a fantasy world) labalaba (a chatterbox) lablab (a tropical bean) lap-lap (a loincloth worn in Papua New Guinea) Laplap (a town in the Philippines) lapo-lapo (?) lapu lapu (a Philippine fish) lau-lau (meat and fish wrapped in leaves and steamed) lava lava (a Samoan loincloth) licky licky (fawning; servile) liqui-liqui (a special kind of Venezuelan jacket) loa loa (?) log log (a kind of graph in which both axes are labeled logarithmically) logi-logi (a stupid person) logo-logo (a stupid person) lolo (?) lomi-lomi (a vigorous Hawaiian massage) low-low (?) Lulu (a name) lulu (something outstanding) mahi-mahi (an edible tropical fish) Mai-Mai (a Congolese militia) Makemake (the third "plutoid", after Pluto and Eris, a dwarf planet beyond Neptune) makomako (a New Zealand wine berry) mama (mother) Matamata (a town in New Zealand) matamata (the South American bearded tortoise) matchy-matchy (descriptive of a decorating or design style that is obsessed with matching) matta-matta (?) Mau Mau (a secretive group that battled for the liberation of Kenya) mek-mek (a persnickety person) mia-mia (a temporary shelter created by an Australian aborigine) mike-mike (a millimeter) Mimi (a name) minny-minny (spots before the eyes, from a blow to the head, or marijuana use) moco moco (a village in Guyana; a town in Bolivia) moko moko (a small New Zealand lizard) momo (a stupid person) mong-mong (a poor white person) mooey mooey (romantic behavior) mopmop (repetitious, unimaginative jazz) motmot (a South American long-tailed passerine bird) mouti mouti (a gossip) mulla mulla (an Australian perennial plant) mulmul (a fine, soft muslin) mumu (?) murmur (a quiet low sound) muru muru (a Brazilian palm oil) muumuu (a loose-fitting Hawaiian dress) my my (an interjection of surprise or disapproval) mymy (an Aborigine's hut) nafnaf (a private language of the Tasaday people in which every word ends in "naf") nan nan (a straw hat) nana (childish word for "banana"; grandma) nar-nar (overdressed, effeminate) nene (the state bird of Hawaii) nebneb (the pods of the North African bablah tree, used for tanning) never never (an imaginary land; a rent-to-own system) Ngaye Ngaye (a town in Somalia) Ngorongoro (an extinct volcano, and park in Tanzania) nit nit! (a warning to keep quiet) no no (something forbidden) nonny nonny (a nonsense phrase used in Shakespeare's songs) nook nook (a young aggressive devotee of acid house music) nulla nulla (an aborigine hardwood war club) nullah nullah (an aborigine hardwood war club) num num (a snack) num nums (breasts) Nyae Nyae (a territory of Namibia) o-o (a Hawaiian bird) the ork-orks (delirium tremens, the trembling mania endured by drunks and druggies) Pago Pago (a Pacific Island) pam pam (a flogging; an argument) Pango Pango (the capital of American Samoa) papa (father) pata pata (sexual intercourse) pawpaw (the papaya tree or wild custardapple) Paw Paw (a town in West Virginia) pee pee (to urinate) Phi Phi (a group of islands in Thailand) picky picky (finicky) pincpinc (the African wren warbler) pip-pip (hello; goodbye) piri piri (a spicy pepper) piupiu (a Maori kilt made of flax) plou-plou (a French private soldier) pompom (a cheerleader's accessory) poo poo (a childish word for excrement) [to] pooh-pooh (to disparage) pousse-pousse (a jinriksha) powpow (conjuration with great ceremony; any noisy assembly) pra-pra (cheating) [to] pre-pre (to suffer from diarrhea) pretty-pretty (a knickknack) puff-puff (?) pupu (a Polynesian appetizer) push push (sexual intercourse) put-put (?) putt putt (the sound of a motor) Qhora Qhora (a town in Bolivia) quack quack (the sound of a duck) quaequae (a Hottentot tribe) quiaquia (the round scad or cigarfish; a tortoise shell rattle) quinaquina (chinchona) rah rah (the sound of cheering; enthusiasm) Rapu-Rapu (an island in the Philippines) rege-rege (rags; ragged clothes) riruriru (the gray warbler of New Zealand) Rongorongo (a mysterious and undeciphered script used on Easter Island) ro-ro (short for "roll on, roll off", a ferry that allows cars or trucks to drive on and off directly) ruru (mopoke) sakkie sakkie (a simple rhythmic Afrikaner musical style) same old same old (nothing has changed) Samsam (a Malay Siamese people) sanga sanga (a tropical African tree) sarsar (a whistling violently cold wind) shweshwe (an African cotton print fabric) see-see (an Asiatic sand partridge) Sen Sen (a sweet candy of long ago, referred to in The Music Man) shabu-shabu (Japanese fondue) she-she (a girl or young woman) shishi (hashish) Sing Sing (a penitentiary in upstate New York) six six six (the sign of the beast) slabba-slabba (big and fat) [to] slam-slam (to salute) so so (mediocre; undistinguished) soft soft (gullible) soosoo (a dolphin of the Ganges river) sous-sous (a particular step in ballet) strumstrum (a crude musical instrument) sucky sucky (fellation) ta ta (farewell) talkee talkee (broken or corrupted speech) tam tam (a kind of drum or gong, made of a large metal saucer hanging in a frame) tangantangan (the castor oil plant) tan-tan (a cow bell) Taqtaq (a town in Iraq) tartar (that stuff the dentist scrapes away; something of which there is a cream) tch-tch (tut tut) tee tee (an Australian diving petrel; a South American squirrel monkey; to urinate; very small) teuf teuf ((suggestive of the sound of a train) - goodbye, I'm off) ticktick (?) tie-tie (?) tika-tika (?) tikitiki (?) tim tim (an unreliable story) titi (a tree of the southern US) toa toa (an ornamental New Zealand pine) toetoe (a tall reedlike New Zealand grass) toi-toi (a tall reedlike New Zealand grass from which you can make a tukutuku; a South African protest dance) tom tom (a primitive drum) too too (excessive; affected) toto (total; in sum) toyi toyi (a South African dance, hopping on one leg, shaking a fist) tsetse (a biting African fly) tsk tsk (a sound of disapproval) tucotuco (a South American rodent, with behavior similar to a mole) tuko-tuko (a tucotuco) tuktuk (a "samlor" of Thailand) tuku-tuku (an ornamental latticework of toi-toi reeds)\ tum tum (baby talk for "stomach") tush-tush (a dismissive or deprecating exclamation) tut tut (an interjection expressing disapproval) tutu (a ballerina's skirt) tweng-tweng (?) twenty twenty (perfect eyesight) twit-twit (?) Ty Ty (a town in Georgia) tzing-tzing (excellent) uffa-uffa (?) uh-uh (?) Ulla Ulla (a town in Bolivia) unk-unks (double unknowns, we don't know if they can happen, and we don't know how to detect them if they did) Vorovoro (an island in Fiji) vuzvuz (a derogatory term for an Ashkenazy Jew) wagga wagga (plentiful) Wagga Wagga (a town in Australia) wagwag (a polishing device used by watchmakers) wah wah (a sound made by a muted trumpet) Walla Walla (a city in Washington state) wang wang (?) wawa (baby talk for "water") [to] wee wee (to urinate) wham-wham (candy from prison vending machines) whoit whoit (the song made by a cardinal) whurra-whurra (?) willy willy (a gusty wind; an Australian cyclone) wonga-wonga (an Australian white-faced pigeon) woo-woo (mystification) Woop Woop (an Australian term for a very rural town) wou wou (?) Woywoy (a town in New South Wales, Australia, where Spike Milligan grew up) Xai-Xai (a town in Mozambique) yang yang (nonsense) yatata yatata (monotonous talking) yaw-yaw (to talk affectedly) yaya (a gum producing tree of Panama) yeye (exuberant) yen yen (a strong craving for narcotics) ylang ylang (a tree) yoyo (a toy) yuk-yuk (empty idle talk) yum-yum (an exclamation of delight) Zam Zam (a town in Sudan) zero zero (extremely poor flying weather, zero ceiling and zero visibility) zig-zig (sexual intercourse) zim-zim (a member of a politically oriented South African gang) zit-zit (?) zoo zoo (the European pigeon; candy from prison vending machines) zou zou (?) Zsa-Zsa (a name) zu-zu (?) zuu-zuu (candy from prison vending machines)
Syllable, Repeat, Rhyme
[the] Boom-Boom Room (a room for sex shows)
atlatl (a primitive spear throwing stick) pronounced "at-lat-l" testes (the male gonads) pronounced "tes-tees"
Thanks to Frank Harmon for blemblem and to Steve Schaefer for corrections and several Hawaiian words.