overnight bag vs overnight case

overnight bag and overnight case both are nouns.

Word	Noun	Adjective	Verb	Adverb
overnight bag	Yes	No	No	No
overnight case	Yes	No	No	No

As nouns, overnight bag and overnight case are synonyms defined as:

overnight bag and overnight case: a small traveling bag to carry clothing and accessories for staying overnight

Other synonyms of overnight bag include overnighter.

overnight bag (noun)	overnight case (noun)
a small traveling bag to carry clothing and accessories for staying overnight	a small traveling bag to carry clothing and accessories for staying overnight