- amphibian (adj.)
- 1630s, "having two modes of existence; of doubtful nature," from Greek amphibia, neuter plural of amphibios "living a double life," from amphi "of both kinds" (see amphi-) + bios "life" (see bio-).
Formerly used by zoologists to describe any sort of animal at home on land and in the water, including crocodiles, walruses, beavers, seals, hippopotami; the restriction to the class of animals between fishes and reptiles with life cycles that begin in water and mature on land is from 1835; Amphibia has been used a zoological classification in this sense since c. 1819.
- amphibian (n.)
- "one of the class of animals between fishes and reptiles, having gills and living in water in the early stage of life, later living on land," 1835; from amphibian (adj.). Amphibia was used in this sense from c. 1600.