AutoAntonyms

An autoantonym is a word or phrase which "contradicts itself"; that is, has two distinct meanings, which are opposite. Such words are sometimes called "Janus words", after the two-headed Roman god, or "antagonyms" or "contranym".

Some examples include:

• ALL OVER: Available everywhere / available no longer.
  "Christmas is all over."
• ANXIOUS: Looking forward to / dreading.
  "How are you feeling about buying Christmas presents?." "Anxious!"
• ARGUE: Assert / deny.
  

  "Few would argue that children are the chief beneficiaries."

  (NYT: 28 May 1999). It is impossible to determine what was meant by this sentence in isolation. It is only from its context that it becomes clear that in this case, the sense of deny was meant.

  "Yet few would argue that the overwhelming contribution of Salinger's life was to American literature and that he is best assessed as a writer and not as a folklore oddity.

  (Salon, 16 January 2012). In this case, the author means to assert the truth of the statement.
• AWFUL: awe-inspiring; derisively bad;
  Her performance as a fertility goddess was awful.
• BACK UP: Going forward / going backward.
  Our student ticket service is back up.
  To get out of the parking spot, I had to back up.
• BEFORE: In order that / Lest. You must dance alone before a boy asks to dance with you.
• BLOWN UP: Magnified / destroyed.
  Because of our great reviews, our department has been blown up.
  Because of our terrible reviews, our department has been blown up.
  
• BUCKLE: To pull together / to fall apart.
• CARRY ON: To behave normally / to behave abnormally.
  When the cat got loose, the teacher carried on.
  When the cat got loose, the children carried on.
• CHARGE: To add to / to take away from.
  My phone went dead, so I charged the battery.
  To pay for the dress, I charged my account.
• CLEAVE: To cut apart / to cling together.
• CONTINUE: To proceed / to interrupt.
  "I wish to continue this argument" means I want the argument to proceed without interruption, unless I am talking to a judge, in which case, I am asking that the argument be halted, to be continued (perhaps!) later.
• DOWNHILL: a better direction / a worse direction.
  I'm afraid it's all downhill from here.
  Luckily, it's all downhill from here.
• DRESS: to add a covering / to remove a covering.
  I dressed the chicken...by removing its feathers.
  I dressed the chicken...by putting a little jacket on it.
• DROP: to terminate / to initiate.
  When Apple dropped the iPhone SE, we were excited to see it.
  When Apple dropped the iPhone SE, we were sorry to see it go.
• DUST: To remove dust / to deposit dust.
  His mother dusted the furniture.
  His mother's ashes dusted the furniture.
• ENJOIN: To forbid / to require.
• EXCEPTIONAL: outstanding / objectionable;
  His moral character is exceptional....he is a saint.
  His moral character is exceptional....he is a notorious sinner.
• FAST: moving quickly / constrained from moving.
  The boat was made fast...by adding a new engine.
  The boat was made fast...by tieing it to the pier.
• FIGHT WITH: fight against / fight alongside of.
  The Afghans fought with the Russians... and stopped them from taking Kabul!
  The Afghans fought with the Russians... and helped them take Kabul!
• FIX: a predicament / a solution.
  The boat was sinking fast...this was a real fix!
  He plugged the hole with chewing gum...this was a real fix!
• FORMAL: merely the outer form / meticulously complete.
  The company didn't mean it; it was only a formal offer.
  If the company really wanted him, they would make a formal offer.
• GIVE OUT: to produce / to fail.
  The ice maker gave out.
  The ice maker gave out...ice.
• GO OFF: Cease operation / begin operation
  "When did the alarm go off?"
  (When did the alarm bell begin to ring?)
  (When did the alarm system fail because the battery ran out?)
• HANDICAP: a disadvantage / an advantange.
  He usually lost at golf because of his handicap.
  He usually won at golf because of his handicap.
• HARDLY: very much; very little;
  The horses were hardly ridden (and hence exhausted.)
  The horses were hardly ridden (and hence out of shape.)
• HOLD: to carry out / to delay.
  The meeting was held for an hour, then everyone left.
  The meeting was held for an hour, til everyone arrived.
• IMPREGNABLE: Unable to be penetrated / able to be impregnated
  Her fortress of chastity is impregnable.
• IN THE WAY OF: Available as / Opposed to
  There is nothing in the way of good will here.
• LEFT: Remaining / departed.
  "How's the enrollment in your class?" "Four students left." (Four students quit the class or only four students remain.)
• LEGENDARY: Famously true / Famously imaginary.
  "Your efficiency is legendary."
• MIRROR IMAGE: Exactly the same / Exactly the opposite.
  His responses were the mirror image of hers.
• NO QUESTION: Yes, certainly / No, certainly.
  "An autumn Romance," he sugggested tentatively. "Was there a question of that?"
  "No question at all."
  "Ah," he said, "I thought as much."
  (The Towers of Trebizond, Rose Macaulay)
• OBLIGE: To require another to do a favor / To do a favor for another.
  "Why was he at the party so long?" "I obliged him." (I required him to stay, as a favor to me, or I let him stay, as a favor to him.)
• ORIGINAL: Very old / very new
  "This is my original idea, but that was years ago."
  "This is my original idea, which has never been expressed before!"
• OVER: Once more / Finished. "This game is over."
  "We'll do this game over."
• OVERLOOK: to inspect / to fail to see.
  I had overlooked the work of my new secretary, so it was perfect.
  I had overlooked the work of my new secretary, which was so error-filled that my boss called me in.
• OVERSIGHT: watching out for errors / failing to see an error.
  It was his oversight that caught the mistake.
  It was his oversight that caused the mistake.
• PARALLEL: separated / related.
  The two schools had everything in common, like parallel worlds.
  The two schools had nothing in common, like parallel worlds.
• PERUSE: To read slowly and carefully / to read quickly.
• PIT: A solid core / a hole.
• PLUG: To fill a hole / to create a hole.
  Who plugged you, cowboy? Doc Watson!
  
• PULLED OFF: achieved, carried out/ cancelled.
  We expect to see the Palestianian elections pulled off.
• RAVEL: To tangle / to untwist.
• REPLACE: restored to its original position / removed from its original position.
  He replaced the telephone receiver - thus hanging up.
  He replaced the telephone receiver - because the old one was cracked.
  (The first usage was observed in "Under the Net" by Iris Murdoch).
• RESIGN: To quit a job / to renew a job contract (re-sign).
  The coach resigned, so we needed to replace him.
  The coach resigned, so we stopped looking for a replacement.
• SANCTION: To bless / to ban.
  The United Nations has sanctioned those shipments.
• SCAN: To read slowly and carefully / to read quickly.
• SCATTER: To add / to get rid of.
  The pope's visit scattered black clouds of despair (since we sadly realized we were all going to be forced to live in a theocracy).
  The pope's visit scattered black clouds of despair (since we joyously realized that the Soviets would now never dare invade).
• SCREEN: to show; to hide;
  The critics screened the movie.
  The critic's head screened the movie, so I couldn't watch it.
• SECRETE: to express (as by a gland); to conceal;
  
• SECURE: to protect from being taken; to obtain from;
  We secured all our silverware from thieves.
• SPAGHETTI: tangled; straight;
  His program is so full of GOTO's it's like spaghetti. As an astronaut approaches a black hole, the tidal forces stretch the body into spaghetti.
• SPARE: extra; meager;
  I received a spare meal from the nun.
• STAY THE COURSE: to stop something from continuing; to continue something;
  We promise to stay the course of tax increases.
• SWALLOW: to accept a requirement; not to make a requirement;
  The union had to swallow the no-strike provision
  The union had to swallow their higher pay demands;
• TOO THIN: too thin / too fat.
  "You can't be too thin for this job."
  (It's impossible to be too thin for this job, so be very thin, or you mustn't be too thin for this job, so be fat.)
• TRIM: To remove excess / to add decorations.
  "We trimmed the Christmas tree..." (by removing excess limbs, or by adding tinsel.)
• UNBARED: exposed / unexposed
  "His soul was unbared." (He did not expose his soul; he did)
• UNQUALIFIED: complete, lacking nothing / lacking all qualification
  "He is an unqualified master..." (He's a master, period / He's a master, but has none of the qualifications necessary to be one.)
• WASTE NO TIME: to do immediately / to not do
  "He wasted no time talking to her..." (He talked to her immediately / He avoided talking to her.)
• WINDUP: to begin or start / to finish
  "The pitcher's windup was remarkable..." (The pitcher's preparation to throw was great / The end of the pitcher's speech was great.)
• YOUNGER: Less aged / occurring earlier in time.
  "These fossils are younger than those..." (meaning they aren't as old, or they were created earlier, and hence are older!)

There is a related, and rather amusing pasttime, which involves picking a word and its opposite, and then finding a path of synonyms that leads from one to the other, using, say, Roget's Thesaurus as arbiter. Thus a hopeful person is expectant, hence anticipating, anxious, fearful, and so in fact despairing!

A tip o' the formal hat to Jumpin' Jeff Borggaard.