What is a contronym?

Contronyms are words that have contradictory meanings, such as:

• “Dust” can mean “to remove dust” or “to cover with dust.”
• “Strike” can mean “to hit” or “to miss (as in baseball).”
• “Moot” can mean “debatable” or “not worth debating.”
• “Weather” can mean “to withstand a storm” or “to be worn away by weather (or time).”
• “Screen” can mean “to show something (like a film)” or “to hide something.”
• “Sanction” can mean “to approve” or “to boycott.”
• “Apology” can mean “an expression of regret” or “a defense or justification.”

“Fast” and “Bound” are similar contronyms:

• “Fast” can mean “move quickly” or “unable to move.”
• “Bound” can mean “heading somewhere” or “unable to move.”

Terms like these are also sometimes called Janus words, named after an ancient Italian deity, regarded as the doorkeeper of heaven and represented as having two faces, one on the back and one on the front of his head. Janus words look both ways thanks to their contradictory meanings. (Incidentally, the month of January is also named after Janus, as it stands at the entrance of the new year.)

Source:

• https://blog.oxforddictionaries.com/2012/06/12/contronyms/