woad vs herb

woad and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
woad	Yes	No	No	No
herb	Yes	No	No	No

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

woad: any of several herbs of the genus Isatis
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 woad include herbaceous plant.

woad (noun)	herb (noun)
any of several herbs of the genus Isatis	aromatic potherb used in cookery for its savory qualities
a blue dyestuff obtained from the woad plant	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests