white-tailed deer vs deer

white-tailed deer and deer both are nouns.

Word	Noun	Adjective	Verb	Adverb
white-tailed deer	Yes	No	No	No
deer	Yes	No	No	No

As nouns, deer is a hypernym of white-tailed deer; that is, deer is a word with a broader meaning than white-tailed deer:

white-tailed deer: common North American deer; tail has a white underside
deer: distinguished from Bovidae by the male's having solid deciduous antlers

Other hypernyms of white-tailed deer include cervid.

white-tailed deer (noun)	deer (noun)
common North American deer; tail has a white underside	distinguished from Bovidae by the male's having solid deciduous antlers