Inherited from Classical Mongolian ᠪᠢ (bi), from Middle Mongol ᠪᠢ (pj /bi/), from Proto-Mongolic *bi (*b- for the first person and *-i for singularity). Cognate with Buryat би (bi), Kalmyk би (bi), Dongxiang bi, etc.
Possibly related somehow with Proto-Turkic *ben and Proto-Tungusic *bi; compare Turkish ben, Evenki би (bi).
Эшлэл: Batsuren, K., Ganbold, A., Chagnaa, A., Giunchiglia, F. Building The Mongolian WordNet. Proceedings of the 10th Global WordNet Conference (GWC), p. 238, 2019.