broad-bean plant vs shell bean

broad-bean plant and shell bean both are nouns.

Word	Noun	Adjective	Verb	Adverb
broad-bean plant	Yes	No	No	No
shell bean	Yes	No	No	No

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

broad-bean plant: Old World upright plant grown especially for its large flat edible seeds but also as fodder
shell bean: a bean plant grown primarily for its edible seed rather than its pod

Other hypernyms of broad-bean plant include shell bean plant.

broad-bean plant (noun)	shell bean (noun)
Old World upright plant grown especially for its large flat edible seeds but also as fodder	unripe beans removed from the pod before cooking
	a bean plant grown primarily for its edible seed rather than its pod