naturally has 3 distinct synonyms spread across 2 of its 4 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 2 recorded opposites are unnaturally, artificially.
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.
according to nature; by natural means; without artificial help
“naturally grown flowers”
in a natural or normal manner
“speak naturally and easily”
Synonyms, antonyms and the broader and narrower relations for naturally come from Princeton University’s WordNet. Full sources and licences.