costumer vs fashion designer

costumer and fashion designer both are nouns.

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

As nouns, fashion designer is a hypernym of costumer; that is, fashion designer is a word with a broader meaning than costumer:

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

Other hypernyms of costumer include clothes designer, couturier, designer.

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