lady's tobacco vs herb

lady's tobacco and herb both are nouns.

Word	Noun	Adjective	Verb	Adverb
lady's tobacco	Yes	No	No	No
herb	Yes	No	No	No

As nouns, herb is a hypernym of lady's tobacco; that is, herb is a word with a broader meaning than lady's tobacco:

lady's tobacco: North American perennial propagated by means of runners
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 lady's tobacco include herbaceous plant.

lady's tobacco (noun)	herb (noun)
North American perennial propagated by means of runners	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