decent has 7 distinct synonyms spread across 4 of its 7 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 indecent.
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.
conforming to conventions of sexual behavior
“speech in this circle, if not always decent, never became lewd”
2 of the 7 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 decent.
Synonyms, antonyms and the broader and narrower relations for decent come from Princeton University’s WordNet. Full sources and licences.