Ranunculus acris vs buttercup

Ranunculus acris and buttercup both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ranunculus acris	Yes	No	No	No
buttercup	Yes	No	No	No

As nouns, buttercup is a hypernym of Ranunculus acris; that is, buttercup is a word with a broader meaning than Ranunculus acris:

Ranunculus acris: perennial European buttercup with yellow spring flowers widely naturalized especially in eastern North America
buttercup: any of various plants of the genus Ranunculus

Other hypernyms of Ranunculus acris include butter-flower, butterflower, crowfoot, goldcup, kingcup.

Ranunculus acris (noun)	buttercup (noun)
perennial European buttercup with yellow spring flowers widely naturalized especially in eastern North America	any of various plants of the genus Ranunculus