unnaturally 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 naturally.
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.
in an unnatural way
“his other arm lay across his chest, unnaturally, as if placed there deliberately, for a purpose”
not according to nature; not by natural means
“artificially induced conditions”
in a manner at variance with what is natural or normal
“The early Church not unnaturally adopted the position that failure to see the messianic character of his work was really caused by the people's own blindness”
Synonyms, antonyms and the broader and narrower relations for unnaturally come from Princeton University’s WordNet. Full sources and licences.