COMMENT: Reconstructed for the PEC level. One is tempted to compare also PN *ʁo-, the present (durative) stem from *-aχ- 'to go', but this raises phonetic problems.
The PC and Av. forms (as well as PL Ablaut grade *ʔoqI:ʷä-) reflect a PEC Ablaut grade *-HumG_wV; in Av. the root is reduplicated.
