pepper grass vs cress

pepper grass and cress both are nouns.

Word	Noun	Adjective	Verb	Adverb
pepper grass	Yes	No	No	No
cress	Yes	No	No	No

As nouns, cress is a hypernym of pepper grass; that is, cress is a word with a broader meaning than pepper grass:

pepper grass: annual herb used as salad green and garnish
cress: any of various plants of the family Cruciferae with edible leaves that have a pungent taste

Other hypernyms of pepper grass include cress plant.

pepper grass (noun)	cress (noun)
annual herb used as salad green and garnish	pungent leaves of any of numerous cruciferous herbs
	any of various plants of the family Cruciferae with edible leaves that have a pungent taste