indecent has 5 distinct synonyms spread across 1 of its 3 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 decent.
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.
not in keeping with accepted standards of what is right or proper in polite society
“was buried with indecent haste”
offensive to good taste especially in sexual matters
“an earthy but not indecent story”
1 of the 3 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 indecent.
Synonyms, antonyms and the broader and narrower relations for indecent come from Princeton University’s WordNet. Full sources and licences.