a domesticated carnivorous mammal that typically has a long snout, an acute sense of smell, non-retractable claws, and a barking, howling, or whining voice. 3 days ago · dog noun [C] (PERSON). Dog definition is - canid; especially : a highly variable domestic mammal (Canis familiaris) closely. A dog is a very common four-legged animal that is often kept by people as a pet or to guard or hunt. Dog definition, a domesticated canid, Canis familiaris, bred in many varieties.