Antonym: a word that is the opposite of another word. For example, "bad" and "good" are antonyms of each other. (The front end comes from "anti," which is against or opposite.)
Homonym: words that sound the same but have different meanings. For instance, "him" and "hymn." One is a person, the other a song. The front end here is from the Greek "homo," which means same and is used in words like "homosexual" and "homogenized."
I've recently been introduced to words that are, thanks to English usage, contronyms, though sometimes that word is spelled "contranym." The front end of the word is, again from the Greek, something that means against, (like "anti") but with the inference of being compared to something else. Contronyms are words also referred to as auto-antonyms.
What they are, in plain language, are words that can have opposite meanings, all by themselves, depending on use and context. They don't depend upon having to have another word like the two examples at the top of the post. Generally, it depends on whether or not the word is being used as a noun or a verb.
You know what? Mental Floss can probably explain it better than I can. They have a short list with further details here.
It cost me 75 cents to put air in my tires the other day. I remember when it was free. I asked the gas station guy why the price had gone up. He replied, "Inflation."
What do you call it when you feed a stick of dynamite to a steer?
Abominable. (Say it slowly to yourself.)
I bet the butcher at my grocery store $50 that he couldn't reach the meat on the top shelf behind him.
He looked and said, "No bet. The steaks are too high."
Did you hear about the numbering snafu on the spaces at the new multi-level parking garage?
It was just wrong on so many levels.
Never hit a man with glasses. It's usually better to use a blunt object.
Oldie but a goodie: What's the difference between roast beef and pea soup?
Well, anybody can roast beef....
Do attorneys have to wear law suits to court?
Mark's Musings is published on a periodical basis - right now on Mondays, Wednesdays, and Fridays - but that may change without notice. Find me on Twitter at http://www.twitter.com/markmusings. This blog is considered to be a digital periodical publication and is filed as such with the U.S. Library of Congress; ISSN 2154-9761.