white rocket vs herb

white rocket and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
white rocket	Yes	No	No	No
herb	Yes	No	No	No

As nouns, herb is a hypernym of white rocket; that is, herb is a word with a broader meaning than white rocket:

white rocket: from Mediterranean region; a naturalized weed throughout southern Europe
herb: a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests

Other hypernyms of white rocket include herbaceous plant.

white rocket (noun)	herb (noun)
from Mediterranean region; a naturalized weed throughout southern Europe	aromatic potherb used in cookery for its savory qualities
	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests