mess vs kettle of fish

mess and kettle of fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
mess	Yes	No	Yes	No
kettle of fish	Yes	No	No	No

As nouns, mess and kettle of fish are synonyms defined as:

Other synonyms of mess include fix, hole, jam, muddle, pickle.

mess (noun)	kettle of fish (noun)
a (large) military dining room where service personnel eat or relax	informal terms for a difficult situation
a meal eaten in a mess hall by service personnel
soft semiliquid food
(often followed by `of') a large number or amount or extent
a state of confusion and disorderliness
informal terms for a difficult situation

mess (verb)	kettle of fish (verb)
make a mess of or create disorder in
eat in a mess hall