aquatic has no recorded synonym. 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 terrestrial, amphibious.
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.
operating or living or growing in water
“boats are aquatic vehicles”
1 of the 3 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for aquatic.
Synonyms, antonyms and the broader and narrower relations for aquatic come from Princeton University’s WordNet. Full sources and licences.