IPA: /ˈkɒstjʊmə/
KK: /ˈkɑːstəmər/
A person or company that makes or provides costumes, especially for performances or events.
The costumer created beautiful outfits for the theater production.
Costumer originates from the Old French word *costumier*, meaning a maker or seller of costumes. The word refers to a person who provides or designs costumes, especially for theatrical performances.
Think of someone who creates or provides 'costumes' — that's what a costumer does.