unnatural has 2 distinct synonyms spread across 2 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 natural.
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 accordance with or determined by nature; contrary to nature
“an unnatural death”
not normal; not typical or usual or regular or conforming to a norm
“abnormal powers of concentration”
speaking or behaving in an artificial way to make an impression
Synonyms, antonyms and the broader and narrower relations for unnatural come from Princeton University’s WordNet. Full sources and licences.