perfect has 18 distinct synonyms spread across 3 of its 5 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 imperfect.
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.
being complete of its kind and without defect or blemish
“a perfect circle”
without qualification; used informally as (often pejorative) intensifiers
“an arrant fool”
a tense of verbs used in describing action that has been completed (sometimes regarded as perfective aspect)
1 of the 5 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for perfect.
Synonyms, antonyms and the broader and narrower relations for perfect come from Princeton University’s WordNet. Full sources and licences.