opposite has 13 distinct synonyms spread across 7 of its 11 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is alternate.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
characterized by opposite extremes; completely opposed
“in diametric contradiction to his claims”
a word that expresses a meaning opposed to the meaning of another word, in which case the two words are antonyms of each other
“to him the antonym of `gay' was `depressed'”
a relation of direct opposition
“we thought Sue was older than Bill but just the reverse was true”
something inverted in sequence or character or effect
“when the direct approach failed he tried the inverse”
directly facing each other
“the two photographs lay face-to-face on the table”
4 of the 11 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for opposite.
Synonyms, antonyms and the broader and narrower relations for opposite come from Princeton University’s WordNet. Full sources and licences.