From Longman Dictionary of Contemporary Englishmastiffmas‧tiff /ˈmæstɪf/ (also bull mastiff) noun [countable] DHPa large strong dog, often used to guard houses
Examples from the Corpus
mastiff• The city's pet-loving Bohemians are obsessed by the horrible death of a woman mauled by a mastiff.• One Sunday, he went hunting with his fierce black mastiffs, stopping only to swig at a flask of strong drink.• A longtime breeder of champion bull mastiffs, Einstein is a smart, able, take-no-prisoners type of gal.• Johno is a 13-stone bull mastiff, Barry's the tiny border terrier.• Ask not what bull mastiffs can do for you.• Two huge gaolers, with the bodies of apes and the faces of cruel mastiffs, padded silently behind them.• A bloody-mouthed mastiff tied by a chain to a lintel of a door snarled and barked.• He stepped over, pierced one of the raw chunks with his dagger and held it up before the mastiff.Origin mastiff (1300-1400) Old French mastin, from Latin mansuetus “easy to handle, not wild” 