mess jacket vs shell jacket

mess jacket and shell jacket both are nouns.

Word	Noun	Adjective	Verb	Adverb
mess jacket	Yes	No	No	No
shell jacket	Yes	No	No	No

As nouns, mess jacket and shell jacket are synonyms defined as:

mess jacket and shell jacket: waist-length jacket tapering to a point at the back; worn by officers in the mess for formal dinners

Other synonyms of mess jacket include monkey jacket.

mess jacket (noun)	shell jacket (noun)
waist-length jacket tapering to a point at the back; worn by officers in the mess for formal dinners	waist-length jacket tapering to a point at the back; worn by officers in the mess for formal dinners