bittercress vs bitter cress

bittercress and bitter cress both are nouns.

Word	Noun	Adjective	Verb	Adverb
bittercress	Yes	No	No	No
bitter cress	Yes	No	No	No

As nouns, bittercress and bitter cress are synonyms defined as:

bittercress and 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

bittercress (noun)	bitter cress (noun)
any of various herbs of the genus Cardamine, having usually pinnate leaves and racemes of white, pink or purple flowers; cosmopolitan except Antarctic	any of various herbs of the genus Cardamine, having usually pinnate leaves and racemes of white, pink or purple flowers; cosmopolitan except Antarctic