The story
Calque from Chinese 西瓜帽 (xīguāmào).
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: A kind of skullcap from China that resembles the rind of half a watermelon, made of six pieces of fabric woven together and a knot on the top, commonly worn by men during the Qing dynasty. Full definition →
Calque from Chinese 西瓜帽 (xīguāmào).
Etymology from Wiktionary, CC BY-SA 4.0.