Contronyms are words that have opposite definitions. The one I always remember is “cleave”—does it mean to join together, or to split apart? Both. Another reason why English is a ridiculously confusing language.
Want more examples? Mental Floss lists fourteen contronyms, and Daily Writing Tips lists 75!
Click those links to check over the lists and see if you have used any of those words ambiguously in your own writing.