afternoon vs greeting

afternoon and greeting both are nouns.

Word	Noun	Adjective	Verb	Adverb
afternoon	Yes	No	No	No
greeting	Yes	No	No	No

As nouns, greeting is a hypernym of afternoon; that is, greeting is a word with a broader meaning than afternoon:

afternoon: a conventional expression of greeting or farewell, used to wish someone a good afternoon
greeting: (usually plural) an acknowledgment or expression of good will (especially on meeting)

Other hypernyms of afternoon include farewell, word of farewell, salutation.

afternoon (noun)	greeting (noun)
a conventional expression of greeting or farewell, used to wish someone a good afternoon	(usually plural) an acknowledgment or expression of good will (especially on meeting)
the part of the day between noon and evening