unconventional has 2 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 conventional.
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 conforming to accepted rules or standards
“her unconventional dress and hair style”
not conventional or conformist
“unconventional life styles”
not conforming to legality, moral law, or social convention
“an unconventional marriage”
Synonyms, antonyms and the broader and narrower relations for unconventional come from Princeton University’s WordNet. Full sources and licences.