hound vs hound dog

hound and hound dog both are nouns.

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

As nouns, hound and hound dog are synonyms defined as:

hound and hound dog: any of several breeds of dog used for hunting typically having large drooping ears

hound (noun)	hound dog (noun)
any of several breeds of dog used for hunting typically having large drooping ears	any of several breeds of dog used for hunting typically having large drooping ears
someone who is morally reprehensible

hound (verb)	hound dog (verb)
pursue or chase relentlessly