sweet woodruff vs herb

sweet woodruff and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet woodruff	Yes	No	No	No
herb	Yes	No	No	No

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

sweet woodruff (noun)	herb (noun)
fragrant dark green leaves used to flavor May wine	aromatic potherb used in cookery for its savory qualities
Old World fragrant stoloniferous perennial having small white flowers and narrow leaves used as flavoring and in sachets; widely cultivated as a ground cover; in some classifications placed in genus Asperula	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests