player vs cosplayer

player and cosplayer both are nouns.

Word	Noun	Adjective	Verb	Adverb
player	Yes	No	No	No
cosplayer	Yes	No	No	No

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

player (noun)	cosplayer (noun)
a theatrical performer	Someone who wears a costume from a comic book or similar media
a person who participates in or is skilled at some game
someone who plays a music as a profession
a person who pursues a number of different social and sexual partners simultaneously
someone who takes part in an activity