Mastiff may refer to: Dog breeds Molosser, a group of several breeds of dog also known as Mastiffs. American Mastiff, a breed of dog in the Molosser group. Bullmastiff, said to be a cross between the English Mastiff and the Bulldog. English Mastiff, a breed of dog in the Molosser group. Spanish Mastiff, an ancient breed of dog originating in Spain. Neapolitan Mastiff, an ancient breed of dog originating in Italy. Tibetan Mastiff, an ancient breed of dog originating in Tibet. Other Mastif… (More on Mastiff)