Contronym
Etymology
A modern coinage: contro- "against" (from Latin "contra") plus -onym "name, word" (from Greek "onoma"). Also called an antagonym, an auto-antonym, or a Janus word — the last after Janus, the two-faced Roman god of doorways and beginnings.
noun · /KON-truh-nim/
A single word that carries two opposite meanings.
What it names
A tidy label for words that quietly contradict themselves — useful when explaining how "sanction," "cleave," or "dust" can each mean a thing and its reverse.
Example
"To sanction" is a perfect contronym: it can mean to permit or to penalize, depending entirely on context.
Related idea
Unlike an oxymoron, which yokes two opposite words into one phrase, a contronym packs both opposites into a single word.