good morning vs salutation

good morning and salutation both are nouns.

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

As nouns, salutation is a hypernym of good morning; that is, salutation 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
salutation: (usually plural) an acknowledgment or expression of good will (especially on meeting)

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

good morning (noun)	salutation (noun)
a conventional expression of greeting or farewell, used to wish someone a good morning	(usually plural) an acknowledgment or expression of good will (especially on meeting)
	an act of honor or courteous recognition
	word of greeting used to begin a letter