French sorrel vs greens

French sorrel and greens both are nouns.

Word	Noun	Adjective	Verb	Adverb
French sorrel	Yes	No	No	No
greens	Yes	No	No	No

As nouns, greens is a hypernym of French sorrel; that is, greens is a word with a broader meaning than French sorrel:

French sorrel: greens having small tart oval to pointed leaves; preferred to common sorrel for salads
greens: any of various leafy plants or their leaves and stems eaten as vegetables

Other hypernyms of French sorrel include green, leafy vegetable.

French sorrel (noun)	greens (noun)
greens having small tart oval to pointed leaves; preferred to common sorrel for salads	any of various leafy plants or their leaves and stems eaten as vegetables
low perennial with small silvery-green ovate to hastate leaves