fancy-dress ball vs masque

fancy-dress ball and masque both are nouns.

Word	Noun	Adjective	Verb	Adverb
fancy-dress ball	Yes	No	No	No
masque	Yes	No	No	No

As nouns, masque is a hypernym of fancy-dress ball; that is, masque is a word with a broader meaning than fancy-dress ball:

Other hypernyms of fancy-dress ball include ball, formal, mask, masquerade, masquerade party.

fancy-dress ball (noun)	masque (noun)
a ball at which guests wear costumes and masks	a party of guests wearing costumes and masks