evening dress vs evening clothes

evening dress and evening clothes both are nouns.

Word	Noun	Adjective	Verb	Adverb
evening dress	Yes	No	No	No
evening clothes	Yes	No	No	No

As nouns, evening dress and evening clothes are synonyms defined as:

evening dress and evening clothes: attire to wear on formal occasions in the evening

Other synonyms of evening dress include eveningwear, formalwear.

evening dress (noun)	evening clothes (noun)
attire to wear on formal occasions in the evening	attire to wear on formal occasions in the evening