evening gown vs dinner gown

evening gown and dinner gown both are nouns.

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

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

Other synonyms of evening gown include dinner dress, formal.

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