tea vs herb tea

tea and herb tea both are nouns.

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

As nouns, herb tea is a hyponym of tea; that is, herb tea is a word with a more specific, narrower meaning than tea:

Other hyponyms of tea include cambric tea, cuppa, cupper, herbal, herbal tea, ice tea, iced tea, sun tea, white tea.

tea (noun)	herb tea (noun)
a beverage made by steeping tea leaves in water	tea-like drink made of leaves of various herbs
a light midafternoon meal of tea and sandwiches or cakes
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