dinner gown vs formalwear

dinner gown and formalwear both are nouns.

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

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

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

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