butterbean vs shell bean

butterbean and shell bean both are nouns.

Word	Noun	Adjective	Verb	Adverb
butterbean	Yes	No	No	No
shell bean	Yes	No	No	No

As nouns, shell bean is a hypernym of butterbean; that is, shell bean is a word with a broader meaning than butterbean:

butterbean (noun)	shell bean (noun)
small flat green bean similar to lima beans	unripe beans removed from the pod before cooking
	a bean plant grown primarily for its edible seed rather than its pod