Auto-antonyms are words with multiple meanings, one of which contradicts or reverses another. What, you say, how can that be? Let's go through a couple examples.
Cleave in the Merriam-Webster dictionary means: a) to adhere firmly and closely, or b) to divide by or as if by a cutting blow.
Think about the word fast and how differently you can use it. Fast is an adjective or adverb meaning "fixed in place, not moving." It also means "moving quickly." Hmmm.
Inflammable technically means "capable of burning or catching aflame," but people often misuse it to mean "unburnable." Yep, flammable and inflammable mean the same thing.
Now consider the word off as in "The tornado siren is going off," which means "to activate." It's also used in "The tornado siren was ringing, but now it's gone off," which means "to deactivate." Hang on, is it ringing or not?
Have you ever buckled your pants together, but your knees buckled apart when you were unnerved or scared? Or have you had oversight on a project you were responsible for, but because of a careless oversight, something important wasn't noticed in time.
Finally, when you clip a lock of hair from your loved one's head, you "separate" it. But when you clip several pages together, you "attach" them.
Auto-antonym or contronym
Back in 1960, Joseph T. Shipley used either auto-antonym and contronym to point out these types of words that do double-duty. The English language being what it is, British English differs in certain meanings from American English, too.
Take, for example, the word table in politics. For Brits, to table a bill means to "put it up for debate." In the US, to table a bill means to "remove it from debate."
Auto-antonyms exist in a variety of languages today. In German, the verb ausleihen can mean either "to borrow" or "to lend." A Romanian verb, inchiria, means "to let" or "to rent," and a Swahili verb, kutoa, means "to add" or "to remove."
Fun auto-antonym examples of translations gone bad
In Hawaiian, people translate the word aloha as both "hello" and "goodbye," when in actuality, it means "love" when used in greetings or farewells.
Everyone's favorite Italian word, ciao, is also translated as "hello" and "goodbye," but its original meaning was "(I am your) slave."
Next time you use an auto-antonym, make sure the other words in your sentence literally make your meaning clear. (See what I did there with literally, which in today's vernacular can mean figuratively.)
There are dozens of other auto-antonyms out there. Let us know in the comments below your favorite ones.