When it is a contronym.
A contranym is defined by Myriam Webster as “a word having two meanings that contradict one another”.
- TRIM – You can trim a tree by adding things to it (decorations)… or you can trim a tree by removing things (branches).
- RESIGN – You can resign from your job and go look for another one… or you can resign a contract to continue with your current job.
- WEATHER – An object can weather a storm and remain intact. Another object could be weather by that same storm and become eroded.
Contronyms are sometimes referred to as Janus words.
“Janus word is a word (such as cleave) having opposite or contradictory meanings depending on the context in which the word is used. Also called antilogy, contronym, contranym, autantonym, auto-antonym, and contradictanyma.”These Words Are Their Own Opposites by Richard Norquist – Aug 2018