Definition of "amphibian"

Of or relating to the class Amphibia.  examples

Capable of operating on both land and water; amphibious.  examples

(obsolete) Having two natures.

An animal of the Amphibia; any four-legged vertebrate that does not have amniotic eggs, living both on land and in water.  examples

A vehicle which can operate on land and water. See Wikipedia article on "Amphibious aircraft"  examples