designer vs costumer

designer and costumer both are nouns.

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

As nouns, costumer is a hyponym of designer; that is, costumer is a word with a more specific, narrower meaning than designer:

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

Other hyponyms of designer include costume designer, costumier.

designer (noun)	costumer (noun)
someone who creates plans to be used in making something (such as buildings)	someone who designs or supplies costumes (as for a play or masquerade)
someone who designs clothing
a person who specializes in interior design
a person who devises plots or intrigues
someone who specializes in graphic design