horse radish vs herb

horse radish and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
horse radish	Yes	No	No	No
herb	Yes	No	No	No

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

horse radish: coarse Eurasian plant cultivated for its thick white pungent root
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 horse radish include herbaceous plant.

horse radish (noun)	herb (noun)
coarse Eurasian plant cultivated for its thick white pungent root	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