evening clothes vs evening dress

evening clothes and evening dress both are nouns.

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

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

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

Other synonyms of evening clothes include eveningwear, formalwear.

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