Webster’s Revised Unabridged Dictionary · 1913
Cerberus
Cer′be·rus (sẽr′bē·rŭs), n. [L. Cerberus (in sense 1), gr. Κέρβερος.]
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. (Zoöl.) A genus of East Indian serpents, allied to the pythons; the bokadam.