Cervus nippon vs deer

Cervus nippon and deer both are nouns.

Word	Noun	Adjective	Verb	Adverb
Cervus nippon	Yes	No	No	No
deer	Yes	No	No	No

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

Cervus nippon: small deer of Japan with slightly forked antlers
deer: distinguished from Bovidae by the male's having solid deciduous antlers

Other hypernyms of Cervus nippon include cervid.

Cervus nippon (noun)	deer (noun)
small deer of Japan with slightly forked antlers	distinguished from Bovidae by the male's having solid deciduous antlers