Ochiai (2025:27–28), following Nakamura (1999:29), treats Ainu kotan as a borrowing from Old Mongolian χotan ‘fortress, city’ and dates its entry to 1271–1296. Nakamura (1999:26, 29–30) presents Mongolian contact in the thirteenth and fourteenth centuries as a possibility and leaves an Ainu origin open. Ikegami (1980:398–400) places kotan within a Mongolian–Manchu–Tungusic–Nivkh diffusion complex. He finds direct borrowing from Uilta or Nivkh difficult because their meanings and uses differ, and leaves the route into Ainu unresolved.