amphibious has 1 distinct synonym spread across 1 of its 2 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 aquatic, terrestrial.
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.
relating to or characteristic of animals of the class Amphibia
operating or living on land and in water
“amphibious vehicles”
Synonyms, antonyms and the broader and narrower relations for amphibious come from Princeton University’s WordNet. Full sources and licences.