fava bean vs bean

fava bean and bean both are nouns.

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

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

fava bean (noun)	bean (noun)
shell beans cooked as lima beans	informal terms for a human head
seed of the broad-bean plant	any of various edible seeds of plants of the family Leguminosae used for food
	any of various leguminous plants grown for their edible seeds and pods
	any of various seeds or fruits that are beans or resemble beans

fava bean (verb)	bean (verb)
	hit on the head, especially with a pitched baseball