Noun 1. a party, dance, or other festive gathering of persons wearing masks and other disguises, and often elegant, historical, or fantastic costumes. 2. a costume or disguise worn at such a gathering. 3. false outward show; façade; pretense. verb 1. to go about under false pretenses or a false character; assume the character of; give oneself out to be. 2. to disguise oneself.