shell jacket vs monkey jacket

shell jacket and monkey jacket both are nouns.

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

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

shell jacket and monkey 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 mess jacket.

shell jacket (noun)	monkey 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