Antonym Dictionary - Antonyms are words with opposed meanings. They are the contrary of synonyms, since synonyms are words that share the same meaning.
So the word ""antonym"" is itself an antonym of the word ""synonym"". And the word ""synonym"" is an antonym of the word ""antonym"", because antonymy is a symmetrical relation: when A is the opposite of B, then B is the opposite of A.
Of course, the meaning of most words cannot be negated, so most words in the language do not have any antonyms.