amphibious:  The Greek prefix amphimeant ‘both, on both sides’ (hence an amphitheatre : Greek and Roman theatres were semicircular, so two joined together, completely surrounding the arena, formed an amphitheatre). Combination with bios ‘life’ (as in biology) produced the Greek adjective amphibios, literally ‘leading a double life’. From the beginning of its career as an English word it was used in a very wide, general sense of ‘combining two completely distinct or opposite conditions or qualities’ (Joseph Addison, for example, used it as an 18th-century equivalent of modern unisex), but that meaning has now almost entirely given way to the word’s zoological application.
At first, amphibious meant broadly ‘living on both land and water’, and so was applied by some scientists to, for example, seals; but around 1819 the zoologist William Macleay proposed the more precise application, since generally accepted, to frogs, newts, and other members of the class Amphibia whose larvae have gills but whose adults breathe with lungs. => biology