red deer vs deer

red deer and deer both are nouns.

Word	Noun	Adjective	Verb	Adverb
red deer	Yes	No	No	No
deer	Yes	No	No	No

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

red deer: common deer of temperate Europe and Asia
deer: distinguished from Bovidae by the male's having solid deciduous antlers

Other hypernyms of red deer include cervid.

red deer (noun)	deer (noun)
common deer of temperate Europe and Asia	distinguished from Bovidae by the male's having solid deciduous antlers