A word having a meaning opposite to that of another word. Antonym is the antonym of synonym.
Antonymy is the sense relation that exists between words which are opposite in meaning. Antonymy is found most commonly (though not exclusively) among adjectives.
Linguists identify three types of antonymy: (1) Gradable antonyms, which operate on a continuum: (very) big, (very) small. Such pairs often occur in binomial phrases with and: (blow) hot and cold, (search) high and low. (2) Complementary antonyms, which express an either/or relationship: dead or alive, male or female. (3) Converse or relational antonyms, expressing reciprocity: borrow or lend, buy or sell, wife or husband."