COMMENT: Reconstructed for the PEC level. Correspondences are regular (although there is a small discrepancy in laryngeal reflexes: we should rather expect in Avar an immobile (A) paradigm corresponding to PN *-ʕ- and PL pharyngealization).
The original meaning must have been "edge, protruding end" preserved in PAA, whence "lip" (PTs) or "forehead" (PL); finally "end" > "game end, set" in PN. EC source is probable for Osset. bɨl / bilä 'lip', see Abayev 1958, 277-278.