amphibian

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various cold-blooded, usually smooth-skinned vertebrates of the class Amphibia, characteristically hatching as an aquatic larva with gills and then transforming into an adult having air-breathing lungs. Frogs, toads, salamanders, and caecilians are amphibians.
• noun An animal capable of living both on land and in water.
• noun An aircraft that can take off and land on either land or water.
• noun A tracked or wheeled vehicle that can operate both on land and in water.

from The Century Dictionary.

• Of or pertaining to amphibia in any sense; specifically, pertaining to the class Amphibia. See amphibious, 2.
• noun An animal of the class Amphibia.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Zoöl.) Of or pertaining to the Amphibia.
• noun (Zoöl.) One of the Amphibia.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective obsolete Having two natures.
• adjective Pertaining to the Amphibia.
• noun An animal of the Amphibia; any four-legged vertebrate that does not have amniotic eggs, living both on land and in water.
• noun A vehicle which can operate on land and water.
• adjective Of or relating to the amphibians Amphibia.
• adjective Capable of operating on both land and water amphibious.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a flat-bottomed motor vehicle that can travel on land or water
• noun cold-blooded vertebrate typically living on land but breeding in water; aquatic larvae undergo metamorphosis into adult form
• adjective relating to or characteristic of animals of the class Amphibia
• noun an airplane designed to take off and land on water