dinner dress vs dinner gown

dinner dress and dinner gown both are nouns.

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

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

Other synonyms of dinner dress include evening gown, formal.

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