overnighter vs suitcase

overnighter and suitcase both are nouns.

Word	Noun	Adjective	Verb	Adverb
overnighter	Yes	No	No	No
suitcase	Yes	No	No	No

As nouns, suitcase is a hypernym of overnighter; that is, suitcase is a word with a broader meaning than overnighter:

overnighter: a small traveling bag to carry clothing and accessories for staying overnight
suitcase: a portable rectangular container for carrying clothes

Other hypernyms of overnighter include bag, grip, traveling bag, travelling bag.

overnighter (noun)	suitcase (noun)
a small traveling bag to carry clothing and accessories for staying overnight	a portable rectangular container for carrying clothes
a guest who stays overnight