buttercup vs herb

buttercup and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
buttercup	Yes	No	No	No
herb	Yes	No	No	No

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

buttercup: any of various plants of the genus Ranunculus
herb: a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests

Other hypernyms of buttercup include herbaceous plant.

buttercup (noun)	herb (noun)
any of various plants of the genus Ranunculus	aromatic potherb used in cookery for its savory qualities
	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests