Comments: PAT *bǝzǝ-jA; PAK *q:a-bzá (Shagirov 1, 218 regards the q:a- as a directive preverb). The root *bza- can also be seen in the compound verb *č:a-bza- 'to get pure, settle (of water)'.
The Ub. form with glottalisation suggests PWC *ṗ-; the PAT reflex *-z- confirms it (if in PWC we had *bǝć̣A, then even after assimilation PAT *-ź- would be expected; on the other hand, *-ź- normally yields PAT *-z-). However, earlier glottalisation must have resided on the affricate, since the initial labial certainly is a historical prefix and there were no glottalised labial prefixes in NC or WC.