Mandaic

bwn - to expound, to explain, to teach (MD 55)

PWS
*byn - to (be) separate(d) (DRS 62; Kogan 2015: 80)
the priority of the verbal root over the nominal formation *bayn- (Lipiński 1997:468) rather than vice versa remains to be substantiated (cf. Blažek 2007:32)