1. vacca — de Vaan
vacca 'cow' [f. a] (Varro+) Has been connected with Skt vasa 'cow' < *uek-eh2 (if PIE), but Latin would require o-grade, and Schrijver has established that *o > a only occurred in open syllables. Thus, the connection cannot be maintained unless one is prepared to reconstruct Pit. *waka- which somehow acquired geminate *-A£-. Muller 1926 suggests a preform *vaka and connects Skt. vasati 'roars' and Lat. vagio. If we … — [de Vaan, s.v. vacca, p. 663]