boarhound vs hound dog

boarhound and hound dog both are nouns.

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

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

boarhound: large hound used in hunting wild boars
hound dog: any of several breeds of dog used for hunting typically having large drooping ears

Other hypernyms of boarhound include hound.

boarhound (noun)	hound dog (noun)
large hound used in hunting wild boars	any of several breeds of dog used for hunting typically having large drooping ears