reptilian

Short definition from Wiktionary

Adjective

1. 1
   Of or relating to the members of the class Reptilia (reptiles).
2. 2
   Reptilelike.
3. 3
   Unthinking, low, base, contemptible.
4. 4
   Cold-blooded, treacherous, unavoidably selfish and hostile.

Noun

1. 1
   A reptilian animal: a reptile.
2. 2
   A reptilian person, especially (ethnic slur) a Jew.
3. 3
   A reptilian alien, especially (ufology, often capitalized) of a shapeshifting race alleged to secretly control the world.