n. a word with multiple definitions, at least two of which directly contradict each other.
Simply put, one of the most fascinating things in the English language. The same word, same spelling, same pronunciation, can mean the opposite of itself. Mostly, this happens when a word has developed a new meaning over time. Additionally, there are many words that seem like auto-antonyms if you use different prepositions with them, but I don’t think that really counts. I’d love to give an example of one, but I’m going to hold off to give them their own entries.