afternoon vs farewell

afternoon and farewell both are nouns.

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

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

afternoon: a conventional expression of greeting or farewell, used to wish someone a good afternoon
farewell: an acknowledgment or expression of goodwill at parting

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

afternoon (noun)	farewell (noun)
a conventional expression of greeting or farewell, used to wish someone a good afternoon	the act of departing politely
the part of the day between noon and evening	an acknowledgment or expression of goodwill at parting