tea vs herb

tea and herb both are nouns.

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

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

tea (noun)	herb (noun)
a beverage made by steeping tea leaves in water	aromatic potherb used in cookery for its savory qualities
a light midafternoon meal of tea and sandwiches or cakes	a plant lacking a permanent woody stem; many are flowering garden plants or potherbs; some having medicinal properties; some are pests
dried leaves of the tea shrub; used to make tea
a tropical evergreen shrub or small tree extensively cultivated in e.g. China and Japan and India; source of tea leaves