fava bean vs shell bean

fava bean and shell bean both are nouns.

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

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

fava bean (noun)	shell bean (noun)
shell beans cooked as lima beans	unripe beans removed from the pod before cooking
seed of the broad-bean plant	a bean plant grown primarily for its edible seed rather than its pod