decorous has 4 distinct synonyms spread across 1 of its 2 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 indecorous.
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 propriety and dignity and good taste in manners and conduct
“the tete-a-tete was decorous in the extreme”
Synonyms, antonyms and the broader and narrower relations for decorous come from Princeton University’s WordNet. Full sources and licences.