meal vs afternoon tea

meal and afternoon tea both are nouns.

Word	Noun	Adjective	Verb	Adverb
meal	Yes	No	No	No
afternoon tea	Yes	No	No	No

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

meal (noun)	afternoon tea (noun)
the food served and eaten at one time	a light midafternoon meal of tea and sandwiches or cakes
coarsely ground foodstuff; especially seeds of various cereal grasses or pulse
any of the occasions for eating food that occur by custom or habit at more or less fixed times