field bean vs shell bean

field bean and shell bean both are nouns.

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

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

field bean: 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 field bean include shell bean plant.

field bean (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