Meaning

noun the attire worn in a play or at a fancy dress ball

noun unusual or period attire not characteristic of or appropriate to the time and place

noun the prevalent fashion of dress (including accessories and hair style as well as garments)

originBorrowed from French costume, from Italian costume, from Latin consuētūdō (“custom, habit”). Doublet of consuetude, custom, and kastom. Verb circa 1802, perhaps modelled on French costumer.

Etymology from Wiktionary, CC BY-SA 3.0