buttercup vs kingcup

buttercup and kingcup both are nouns.

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

As nouns, buttercup and kingcup are synonyms defined as:

Other synonyms of buttercup include butter-flower, butterflower, crowfoot, goldcup.

buttercup (noun)	kingcup (noun)
any of various plants of the genus Ranunculus	any of various plants of the genus Ranunculus
	swamp plant of Europe and North America having bright yellow flowers resembling buttercups