Comments:All forms reflect a suffixed *ènŋù-kV. A certain phonetic problem is raised by u- in Mong.; one has to assume PM *unu-gan (cf. the early TM loans: Evk. unukān 'foal', Sol. unuxũ 'kid'; see on it Poppe 1974, 128) with vocalic assimilation from earlier *anu-gan. Otherwise the etymology seems quite plausible, and appears to explain the Jpn. form better than the usual theory of Chinese borrowing (neither MC mạ́, nor OC mrāʔ can explain the initial um- in Japanese).