salutation vs acknowledgement

salutation and acknowledgement both are nouns.

Word	Noun	Adjective	Verb	Adverb
salutation	Yes	No	No	No
acknowledgement	Yes	No	No	No

As nouns, acknowledgement is a hypernym of salutation; that is, acknowledgement is a word with a broader meaning than salutation:

salutation: (usually plural) an acknowledgment or expression of good will (especially on meeting)
acknowledgement: a statement acknowledging something or someone

Other hypernyms of salutation include acknowledgment.

salutation (noun)	acknowledgement (noun)
(usually plural) an acknowledgment or expression of good will (especially on meeting)	a statement acknowledging something or someone
an act of honor or courteous recognition	the state or quality of being recognized or acknowledged
word of greeting used to begin a letter