dinner dress vs eveningwear

dinner dress and eveningwear both are nouns.

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

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

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

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