Comments:Korean has a usual loss of narrow vowel between a stop and a fricative. The back row in PT is not quite regular (*büs- would be expected). It might be better to reconstruct *biso ( > Turk. *bɨs-, with a subsequent labial assimilation > *bus-). In TM cf. perhaps Nan. busĩ 'rodents' stores' (ТМС 1, 115).