mastiff, breed of very large, powerful working dog developed in England more than 2,000 years ago. It stands from 27 to 33 in. (68.6-83.8 cm) high at the shoulder and weighs from 165 to 185 lb (74.9-83.9 kg). Its coarse, short, close-lying coat may be silver fawn, apricot, or dark fawn brindle in color, with a black muzzle, nose, and ears and black around the eyes. The mastiff was first bred as a fighting dog and guardian. As a fighter it was cited for its physical prowess and courage by Caesar in his account of the Roman invasion of Britain in 55 B.C. Indeed, it was later imported to Rome to fight in the arena. In its native country the mastiff was a popular antagonist in bullbaiting and bearbaiting contests and in organized dogfights until these blood sports were outlawed in 1835. However, throughout the entire history of the breed in England its greatest popularity has derived from its widespread use as a guardian of home and family. This centuries-old association with man is undoubtedly responsible for the mastiff's unexcelled suitability for the role of family companion and its particular devotion to and gentleness with children. The term mastiff is also applied to a general type of giant dog whose origin has been traced to Asia and of which the modern Tibetan mastiff, infrequently seen in the United States, is representative. See dog.

Breed of powerful but gentle dog of Europe and Asia dating to 3000 BC. Mastiffs fought bears, lions, tigers, bulls, and gladiators in Roman arenas and were used in English bull- and bear-baiting rings. The mastiff stands 28–30 in. (70–75 cm) tall and weighs 165–185 lbs (75–85 kg). It has a broad head, short dark muzzle, and dark drooping ears. Its short coat is apricot, silver fawn, or brindled. The bullmastiff, a bulldog-mastiff crossbreed standing 24–27 in. (61–69 cm) tall and weighing 100–130 lbs (45–59 kg), is used as a police and guard dog.

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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.
• Dogue de Bordeaux, Bordeaux Mastiff or French Mastiff is one of the most ancient French breeds.
• Pug, a dog of the Toy Group, considered by some to be a miniature breed of mastiff, originating in China.
• Cane Corso, a mastiff that originated in Italy.

Other

• Mastiff UAV - a battlefield UAV built by Tadiran Electronic Industries.
• Mastiff Tech (Software Product Development Company)
• Mastiff (company) - video game company.
• The British Army designation for the Cougar AFV