buttercup vs herbaceous plant

buttercup and herbaceous plant both are nouns.

Word	Noun	Adjective	Verb	Adverb
buttercup	Yes	No	No	No
herbaceous plant	Yes	No	No	No

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

buttercup: any of various plants of the genus Ranunculus
herbaceous plant: 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 herb.

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