black currant vs currant bush

black currant and currant bush both are nouns.

Word	Noun	Adjective	Verb	Adverb
black currant	Yes	No	No	No
currant bush	Yes	No	No	No

As nouns, currant bush is a hypernym of black currant; that is, currant bush is a word with a broader meaning than black currant:

black currant: widely cultivated currant bearing edible black aromatic berries
currant bush: any of various deciduous shrubs of the genus Ribes bearing currants

Other hypernyms of black currant include currant.

black currant (noun)	currant bush (noun)
small black berries used in jams and jellies	any of various deciduous shrubs of the genus Ribes bearing currants
widely cultivated currant bearing edible black aromatic berries