tea vs black tea

tea and black tea both are nouns.

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

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

Other hyponyms of tea include tea bag, green tea, oolong.

tea (noun)	black tea (noun)
a beverage made by steeping tea leaves in water	fermented tea leaves
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