messmate vs acquaintance

messmate and acquaintance both are nouns.

Word	Noun	Adjective	Verb	Adverb
messmate	Yes	No	No	No
acquaintance	Yes	No	No	No

As nouns, acquaintance is a hypernym of messmate; that is, acquaintance is a word with a broader meaning than messmate:

messmate: (nautical) an associate with whom you share meals in the same mess (as on a ship)
acquaintance: a person with whom you are acquainted

Other hypernyms of messmate include friend.

messmate (noun)	acquaintance (noun)
(nautical) an associate with whom you share meals in the same mess (as on a ship)	personal knowledge or information about someone or something
	a person with whom you are acquainted
	a relationship less intimate than friendship