dinner gown vs evening clothes

dinner gown and evening clothes both are nouns.

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

As nouns, evening clothes is a hypernym of dinner gown; that is, evening clothes is a word with a broader meaning than dinner gown:

Other hypernyms of dinner gown include evening dress, eveningwear, formalwear, gown.

dinner gown (noun)	evening clothes (noun)
a gown for evening wear	attire to wear on formal occasions in the evening