dirty has 22 distinct synonyms spread across 10 of its 13 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 clean.
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.
(of behavior or especially language) characterized by obscenity or indecency
“dirty words”
spreading pollution or contamination; especially radioactive contamination
“the air near the foundry was always dirty”
2 of the 13 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 dirty.
Synonyms, antonyms and the broader and narrower relations for dirty come from Princeton University’s WordNet. Full sources and licences.