Source : Webster's Revised Unabridged Dictionary (1913)

Reptilia \Rep*til"i*a\ (r?p-t?l"?-?), n.pl. [NL.] (Zo["o]l.)
   A class of air-breathing oviparous vertebrates, usually
   covered with scales or bony plates. The heart generally has
   two auricles and one ventricle. The development of the young
   is the same as that of birds.

   Note: It is nearly related in many respects to Aves, or
         birds. The principal existing orders are Testidunata or
         Chelonia (turtles), Crocodilia, Lacertilla (lizards),
         Ophidia (serpents), and Rhynchocephala; the chief
         extinct orders are Dinosauria, Theremorpha, Mosasauria,
         Pterosauria, Plesiosauria, Ichtyosauria.

Source : WordNet®

Reptilia
     n : class of cold-blooded air-breathing vertebrates with
         completely ossified skeleton and a body usually covered
         with scales or horny plates; once the dominant land
         animals [syn: {class Reptilia}]