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).
Por que os cães são chamados de cães?
Há cerca de sete séculos, a palavra "hound", que veio do antigo inglês hund, era a palavra para todos os cães domésticos. Cão era usado apenas para se referir a um subgrupo de cães que inclui o encantador mas freqüentemente salivar mastigar. Claro, o oposto é verdade agora. Usamos cão para falar sobre todos os melhores amigos do homem, de adoráveis golden retrievers para panting chow chows. E cão é usado agora para indicar um tipo de cão usado apenas para caça.