The Collaborative International Dictionary of English v.0.48:

Cerastes \Ce*ras"tes\, n. [L., a horned serpent, fr. Gr.
   kera`sths horned, fr. ke`ras horn.] (Zool.)
   A genus of poisonous African serpents, with a horny scale
   over each eye; the horned viper.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cerastes
    n 1: highly venomous viper of northern Africa and southwestern
         Asia having a horny spine above each eye [syn: horned
         viper, cerastes, sand viper, horned asp, Cerastes
         cornutus]