an ‧ to ‧ nym /ˈæntənɪm/ BrE AmE noun [countable]
[ Date: 1800-1900 ; Language: French ; Origin: antonyme , from Greek anti- ( ⇨ ↑ anti- ) + onyma 'name' ]
a word that means the opposite of another word ⇨ synonym :
a dictionary of synonyms and antonyms