tea vs tea bag

tea and tea bag both are nouns.

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

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

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

tea (noun)	tea bag (noun)
a beverage made by steeping tea leaves in water	small paper bag holding a measure of tea
a light midafternoon meal of tea and sandwiches or cakes	a measured amount of tea in a bag for an individual serving of tea
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