pepper root vs bitter cress

pepper root and bitter cress both are nouns.

Word	Noun	Adjective	Verb	Adverb
pepper root	Yes	No	No	No
bitter cress	Yes	No	No	No

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

pepper root: North American herb with pungent scaly or toothed roots
bitter cress: any of various herbs of the genus Cardamine, having usually pinnate leaves and racemes of white, pink or purple flowers; cosmopolitan except Antarctic

Other hypernyms of pepper root include bittercress.

pepper root (noun)	bitter cress (noun)
North American herb with pungent scaly or toothed roots	any of various herbs of the genus Cardamine, having usually pinnate leaves and racemes of white, pink or purple flowers; cosmopolitan except Antarctic