green bean vs bean

green bean and bean both are nouns.

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

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

green bean: seed of the mung bean plant used for food
green bean: food from the seed of the mung bean plant
bean: any of various edible seeds of plants of the family Leguminosae used for food

Other hypernyms of green bean include edible bean.

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

green bean (noun)	bean (noun)
immature bean pod eaten as a vegetable	informal terms for a human head
seed of the mung bean plant used for food; food from the seed of the mung bean plant	any of various edible seeds of plants of the family Leguminosae used for food
a common bean plant cultivated for its slender green edible pods	any of various leguminous plants grown for their edible seeds and pods
seed of the mung bean plant; used for food; seed of the mung bean plant	any of various seeds or fruits that are beans or resemble beans

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