A contronym (also spelled "contranym") and also known as an auto-antonym (also spelled "autantronym") is "a word with a homograph (another word of the same spelling) which is also an antonym (a word with the opposite meaning)," Wikipedia tells us.
Wikipedia goes on, even more helpfully, to tell us, "An auto-antonym is alternatively called an antagonym, Janus word (after the Roman god), enantiodrome, self-antonym, antilogy, or addad (Arabic, singular didd).
It is a word with multiple meanings, one of which is defined as the
reverse of one of its other meanings. This phenomenon is called enantiosemy, enantionymy or antilogy."
I just read the word "contronym" for the first time in an online article about how people misuse the word "literally." (Here's the article, "The Word We Love to Hate. Literally.") (This article was first posted online about nine years ago. Why did I just find it today? I don't know.) The fifth paragraph covers other contronyms, or words "used in a seemingly contradictory way."
I especially liked the article's treatment of the word "paraphrase." When people say, for instance, "To paraphrase Gertrude Stein, 'A tricycle is a tricycle is a tricycle,'" they're not really paraphrasing Gertrude Stein's famous statement about the nature of roses. If you wanted to paraphrase that, you would say something like, "Roses are all roses, nothing more, nothing less."
Anyway, in case the Wikipedia article stuns and distracts you as much as it does me, here's a story about the "topsy-turvy world" of contronyms.
And here's a Web page with a fascinating list of contronyms. Check it out! These examples are what finally helped me understand what contronyms are.