Dictionary.com Thesaurus.com

mastiff vs. bullmastiff

mastiff

[mas-tif, mah-stif] / ˈmæs tɪf, ˈmɑ stɪf /

noun

one of a breed of large, powerful, short-haired dogs having an apricot, fawn, or brindled coat.

bullmastiff

[bool-mas-tif, -mah-stif] / ˈbʊlˈmæs tɪf, -ˈmɑ stɪf /

Or bull-mastiff,

one of an English breed of dogs having a short, fawn or brindled coat, produced by crossing the bulldog and the mastiff.