Amphibian (animal), animal with moist, hairless skin through which water can pass in and out. Nearly all amphibians live the first part of their lives in water and the second part on land—a double life reflected in the name amphibian, which comes from the Greek words amphi, meaning “both,” and bios, meaning “life.” Amphibians were the first animals with backbones to adapt to life on land. They are the ancestors of reptiles, which in turn gave rise to mammals and birds. (Source: MSN Encarta )