formalwear vs evening dress

formalwear and evening dress both are nouns.

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

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

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

Other synonyms of formalwear include evening clothes, eveningwear.

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