good morning vs farewell

good morning and farewell both are nouns.

Word	Noun	Adjective	Verb	Adverb
good morning	Yes	No	No	No
farewell	Yes	No	No	No

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

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

Other hypernyms of good morning include word of farewell, greeting, salutation.

good morning (noun)	farewell (noun)
a conventional expression of greeting or farewell, used to wish someone a good morning	the act of departing politely
	an acknowledgment or expression of goodwill at parting