The Collaborative International Dictionary of English v.0.48:

Reptilia \Rep*til"i*a\ (r?p-t?l"?-?), n. pl. [NL.] (Zool.)
   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.
   [1913 Webster]

   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.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Reptilia
    n 1: 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: Reptilia, class Reptilia]