Source : Webster's Revised Unabridged Dictionary (1913)

Cerberus \Cer"be*rus\, n. [L. Cerberus (in sense 1), gr. ?.]
   1. (Class. Myth.) A monster, in the shape of a three-headed
      dog, guarding the entrance into the infernal regions,
      Hence: Any vigilant custodian or guardian, esp. if surly.

   2. (Zo["o]l.) A genus of East Indian serpents, allied to the
      pythons; the bokadam.

Source : WordNet®

Cerberus
     n : (Greek mythology) 3-headed dog guarding the entrance to
         Hades; son of Typhon [syn: {hellhound}]