The Collaborative International Dictionary of English v.0.48:

Reptilian \Rep*til"i*an\, n. (Zool.)
   One of the Reptilia; a reptile.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Reptilian \Rep*til"i*an\ (-an), a.
   Belonging to the reptiles.
   [1913 Webster]

   Reptilian age (Geol.), that part of geological time
      comprising the Triassic, Jurassic, and Cretaceous periods,
      and distinguished as that era in which the class of
      reptiles attained its highest expansion; -- called also
      the Secondary or Mezozoic age.
      [1913 Webster]

WordNet (r) 3.0 (2006):

reptilian
    adj 1: of or relating to the class Reptilia
    n 1: any cold-blooded vertebrate of the class Reptilia including
         tortoises, turtles, snakes, lizards, alligators,
         crocodiles, and extinct forms [syn: reptile, reptilian]

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "reptilian":
   abject, abominable, alligator, amphibian, anguine, arrant,
   atrocious, base, batrachian, beggarly, cheesy, colubriform,
   contemptible, crawling, creeping, crocodile, crocodilian, crummy,
   debased, degraded, depraved, despicable, dinosaur, dirty,
   disgusting, execrable, flagrant, foul, froggy, fulsome, gator,
   grave, gross, heinous, little, lizard, lizardlike, low, low-down,
   lumpen, mangy, mean, measly, miserable, monstrous, nefarious,
   obnoxious, odious, ophidian, paltry, petty, poky, poor, rank,
   repent, reptant, reptile, reptilelike, reptiliform, reptiloid,
   saurian, scabby, scrubby, scruffy, scummy, scurvy, serpentiform,
   serpentile, serpentine, serpentlike, serpentoid, shabby, shoddy,
   slithering, small, snakelike, snaky, squalid, terrapin, toadish,
   tortoise, turtle, unmentionable, vile, viperiform, viperish,
   viperlike, viperoid, viperous, vipery, wretched