beet green vs leafy vegetable

beet green and leafy vegetable both are nouns.

Word	Noun	Adjective	Verb	Adverb
beet green	Yes	No	No	No
leafy vegetable	Yes	No	No	No

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

beet green: young leaves of the beetroot
leafy vegetable: any of various leafy plants or their leaves and stems eaten as vegetables

Other hypernyms of beet green include green, greens.

beet green (noun)	leafy vegetable (noun)
young leaves of the beetroot	any of various leafy plants or their leaves and stems eaten as vegetables