shell jacket vs mess jacket

shell jacket and mess jacket both are nouns.

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

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

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

Other synonyms of shell jacket include monkey jacket.

shell jacket (noun)	mess 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