What does コスプレ Cosplay mean?

Cosplay is a Japanese word made out of English. It was coined in Japan, and its first appearance in print can be dated, which is unusual: most vocabulary has no birth certificate and this one nearly does.

The coinage

Nobuyuki Takahashi, of Studio Hard, and some university friends were writing a magazine article about fans who dressed as manga and anime characters at Comiket in Tokyo. They needed a term.

Masquerade was the Western word, and translated into Japanese it sounded, in Takahashi's words, "too noble and old fashioned". A Japanese word for dressing up already existed, kasou, but it carried a nuance of disguise.

So they assembled one from costume and play. The article used both the long form, costume play, and the short コスプレ, and a year or two later the short form was in wide use among fans at conventions.

Why play was the right half

Because it points at performance rather than clothing. A costume is a garment; playing is something a person does. The word claims that the practice is closer to acting than to dressing up, and that claim has held: the culture that grew around it cares about pose, expression and character, and treats the outfit as equipment rather than as the point.

English masquerade could not have carried that.

The return journey

English then took it back. The word now appears in English dictionaries and is used fluently by people who have never encountered Japanese, describing an activity that predates the term by decades in the English-speaking world.

So English fandom was doing this before the word existed, and adopted a Japanese coinage to name its own long-standing practice. That is a more interesting history than either language usually gets credit for.

What the case demonstrates

That wasei-eigo is not a defective form of English. A Japanese writer and his friends found the Japanese rendering of an English word unsuitable, built a new one out of English parts, and the English-speaking world eventually took it.