plumbago vs herb

plumbago and herb both are nouns.

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

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

plumbago: any plumbaginaceous plant of the genus Plumbago
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 plumbago include herbaceous plant.

plumbago (noun)	herb (noun)
any plumbaginaceous plant of the genus Plumbago	aromatic potherb used in cookery for its savory qualities
used as a lubricant and as a moderator in nuclear reactors	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests