costumer vs costume designer

costumer and costume designer both are nouns.

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

As nouns, costumer and costume designer are synonyms defined as:

costumer and costume designer: someone who designs or supplies costumes (as for a play or masquerade)

Other synonyms of costumer include costumier.

costumer (noun)	costume designer (noun)
someone who designs or supplies costumes (as for a play or masquerade)	someone who designs or supplies costumes (as for a play or masquerade)