Contronyms

I first came across the term contronym when I was teaching middle school English. They are words that are their own antonyms. In other words, they mean something and they mean the opposite. That can be confusing.

Take this sentence:  "The company's oversight had become a costly issue."  Did the company overlook a problem or was it that their conscientious overseeing of something was costing someone problems?

Usually, we can tell which meaning from the context.  "The carcass was cleaved" uses it to mean "to plit or sever" (as with a cleaver).  "He cleaves to his beliefs" means not a split but that he clings or adheres to them. Both meanings come from Old English, but from different, though similar words.  Cleave as to adhere comes from clifian. Cleave as in to split comes from clēofan. That word takes forms that apply to that meaning still, like "cloven," as in a type of split hoof and "cleft" as in cleft palate.

Some other contronyms:

Sanction = to give official permission or approval OR to impose a penalty on.

Left = remaining (What's left to eat?) OR departed (Everyone left the room.)

Dust = the noun is that annoying coating on furniture, but the verb is to remove that coating. Similarly, we use "seed." Seeding the lawn adds seeds but seeding a pepper is removing them.

Trim as a verb can mean adding or taking away. If you trim the Christmas tree, you add decorations. But if you trim a tree in the backyard, you are more likely to be cutting away at it.

Fast can mean "moving rapidly" (driving fast) or "fixed, unmoving" (holding fast or colors that are fast and so will not run).

Screen can mean ‘to show’ (a movie) or ‘to hide’ (an unsightly view).

Clip can mean "to bind together" (clip some papers) or "to separate" (as in clippers or clipping coupons from a newspaper).