Why are dogs called dogs?
About seven centuries ago, the word hound, which came from the Old English hund, was the word for all domestic canines. Dog was just used to refer to a subgroup of hounds that includes the lovely but frequently slobbering mastiff.

Of course, the opposite is now true. We use dog to talk about all of man’s best friends, from lovable golden retrievers to panting chow chows. And hound is now used to indicate a type of dog used just for hunting. Hound especially refers to a dog with a long face and large, droopy ears. Linguists still speculate about the reversal of fortune for hound and dog. One idea suggests that the sub-breed known as dogs became so populous that dog simply became the generic term (sort of an animal equivalent of the way brand names can become so ubiquitous that they start to be used as a general term for their purpose).