formal vs masked ball

formal and masked ball both are nouns.

Word	Noun	Adjective	Verb	Adverb
formal	Yes	Yes	No	No
masked ball	Yes	No	No	No

As nouns, masked ball is a hyponym of formal; that is, masked ball is a word with a more specific, narrower meaning than formal:

Other hyponyms of formal include cotilion, cotillion, fancy-dress ball, masquerade ball, prom, promenade.

formal (noun)	masked ball (noun)
a gown for evening wear	a ball at which guests wear costumes and masks
a lavish dance requiring formal attire

formal (adjective)	masked ball (adjective)
being in accord with established forms and conventions and requirements (as e.g. of formal dress)
(of spoken and written language) adhering to traditional standards of correctness and without casual, contracted, and colloquial forms
refined or imposing in manner or appearance; befitting a royal court
logically deductive
represented in simplified or symbolic form
characteristic of or befitting a person in authority