formalwear vs evening clothes

formalwear and evening clothes both are nouns.

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

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

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

Other synonyms of formalwear include evening dress, eveningwear.

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