mastiff

noun1

1. •
   One of an old breed of powerful, deep-chested, and smooth-coated dogs, used chiefly as watchdogs and guard dogs.

   • Avaunt, you curs! Be thy mouth or black or white, Tooth that poisons if it bite; Mastiff, greyhound, mongrel grim, Hound or spaniel, brach or him. — 1603