onsen

The story

1. Middle Chinese · derived from溫泉“hot springs”
2. Japanese · derived from温泉
3. English todayonsen

From Japanese 温泉 (onsen), from Middle Chinese 溫泉 ('won dzjwen, “hot springs”), from 溫 /温 (wēn, “warm”) + 泉 (quán, “spring[s]”). Compare the modern Mandarin pronunciation 溫泉 /温泉 (wēnquán).