Definitions of costume:

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

  Example: "He won the prize for best costume"

• noun:   the attire characteristic of a country or a time or a social class

  Example: "He wore his national costume"

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

  Example: "In spite of the heat he insisted on his woolen costume"

• noun:   the prevalent fashion of dress (including accessories and hair style as well as garments)
• verb:   furnish with costumes; as for a film or play
• verb:   dress in a costume