A costume is a type of clothing that a person wears when celebrating a holiday, when pretending to be another person for a performance, or when promoting an activity or a business:
The mascot for that team is wearing a bird costume.
Kids come to the door dressed in costumes on Halloween and ask for candy.
The actors and actresses who performed in the play wore costumes from the 16th century.
Costumes are easily found at thrift stores and consignment shops.
Our neighbors down the street had a party and everyone came wearing a costume.
To celebrate a special holiday, the people of the town wear viking costumes.
