Abarim Publications' online Biblical Hebrew Dictionary
The root-verb ביי (bayay) or בי (bay) means to entreat. As verb it only occurs in Job 34:36, but it yields בי (bi), which a particle of entreaty. Contrasted by the more common particle of entreaty נא (na, as in Hosanna), our word בי (bi) is reserved for expressing "craving permission to address a superior, always followed by אדני (adonai) and always (except Joshua 7:8) at the beginning of a speech" (in the words of BDB Theological Dictionary). It means something like "I pray . . . ," or "excuse me . . . "