A word that can be its own opposite. I learned this from Kathryn Schulz’ excellent article, What part of “No, totally” don’t you understand, about how “no, totally” came to mean “yes.” Contranyms — like heteronyms, portemanteaus, palindromes, and semordnilaps — are neat things to look out for. Like how you can dust something to pick up dust from a surface, and dust that surface to remove dust from it. So versatile. Or perhaps confusing.