wolfhound vs hound dog

wolfhound and hound dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
wolfhound	Yes	No	No	No
hound dog	Yes	No	No	No

As nouns, hound dog is a hypernym of wolfhound; that is, hound dog is a word with a broader meaning than wolfhound:

wolfhound: the largest breed of dogs; formerly used to hunt wolves
hound dog: any of several breeds of dog used for hunting typically having large drooping ears

Other hypernyms of wolfhound include hound.

wolfhound (noun)	hound dog (noun)
the largest breed of dogs; formerly used to hunt wolves	any of several breeds of dog used for hunting typically having large drooping ears