mustard greens vs mustard

mustard greens and mustard both are nouns.

Word	Noun	Adjective	Verb	Adverb
mustard greens	Yes	No	No	No
mustard	Yes	No	No	No

As nouns, mustard greens and mustard are synonyms defined as:

Other synonyms of mustard greens include Indian mustard, leaf mustard.

mustard greens (noun)	mustard (noun)
leaves eaten as cooked greens	pungent powder or paste prepared from ground mustard seeds
	leaves eaten as cooked greens
	any of several cruciferous plants of the genus Brassica