dinner gown vs dinner dress

dinner gown and dinner dress both are nouns.

Word	Noun	Adjective	Verb	Adverb
dinner gown	Yes	No	No	No
dinner dress	Yes	No	No	No

As nouns, dinner gown and dinner dress are synonyms defined as:

Other synonyms of dinner gown include evening gown, formal.

dinner gown (noun)	dinner dress (noun)
a gown for evening wear	a gown for evening wear