eveningwear vs evening dress

eveningwear and evening dress both are nouns.

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

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

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

Other synonyms of eveningwear include evening clothes, formalwear.

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