*uerso- — de Vaan
*uerso- 'peak', Skt. varsman- [n.] 'height, top' < *uers-mn-, varsistha- 'highest, most excellent'; Lith. virsus [m.], Latv. virsus, OCS vrweb, Ru, verx, loc.sg. verxu 'top, upper part' < *ufs-u-; OE wearr csilP. Uncertain: Go. wairsiza, OHG wirsiro 'worse' < *uersizon-. The suffix -ucus can be denominal to a stem in *-w-, but it is also found after other types of stems. The original ablaut grade of the root cannot … — [de Vaan, s.v. *uerso-, p. 680]