dinner dress vs formalwear

dinner dress and formalwear both are nouns.

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

As nouns, formalwear is a hypernym of dinner dress; that is, formalwear is a word with a broader meaning than dinner dress:

Other hypernyms of dinner dress include evening clothes, evening dress, eveningwear, gown.

dinner dress (noun)	formalwear (noun)
a gown for evening wear	attire to wear on formal occasions in the evening