costume vs costumer

costume and costumer both are nouns.

Word	Noun	Adjective	Verb	Adverb
costume	Yes	No	Yes	No
costumer	Yes	No	No	No

costume (noun)	costumer (noun)
the attire worn in a play or at a fancy dress ball	someone who designs or supplies costumes (as for a play or masquerade)
the attire characteristic of a country or a time or a social class
unusual or period attire not characteristic of or appropriate to the time and place
the prevalent fashion of dress (including accessories and hair style as well as garments)

costume (verb)	costumer (verb)
dress in a costume
furnish with costumes; as for a film or play