afternoon vs word of farewell

afternoon and word of farewell both are nouns.

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

As nouns, word of farewell is a hypernym of afternoon; that is, word of 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
word of farewell: an acknowledgment or expression of goodwill at parting

Other hypernyms of afternoon include farewell, greeting, salutation.

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