vacca.

Uncertain. It could be connected with Sanskrit वशा (vaśā), perhaps suggesting a PIE form *weḱ-éh₂. However, this theory does not explain the /a/ in the Latin form. Perhaps a Proto-Indo-European form *woḱéh₂ may also be reconstructed. However, De Vaan argues that Latin /a/ only emerged from Proto-Italic /o/ in open syllables. Alternatively, it may derive from a form *wākā and be connected to Sanskrit वाशति (vā́śati, “to roar”) and Latin vāgiō Based on this connection, De Vaan postulates a root *weh₂- and proposes that the Latin term may have semantically evolved from a pre-form with a meaning akin to "the bellowing one." Another possibility is that the term is related to the root Proto-Indo-European *weh₂g- (“to make a harsh sound”). However, in both proposals the origin of the consonant gemination (i.e. the ) is disputed. The classicist William F. Wyatt Jr. doubts the connection to Sanskrit वशा (vaśā), noting that—although the Sanskrit term can mean cow—it can also mean "barren". According to Wyatt, the differing meanings contradict a shared ancestor. Furthermore, Wyatt argues that it is unusual for Latin terms related to agriculture to have Sanskrit cognates, as—according to Wyatt—the majority of the shared vocabulary between the languages is related to religion or law. Moreover, Wyatt suggests that if the terms did originate from Proto-Indo-European, it is likely the common ancestor would only refer to female cattle. Wyatt considers it unusual for a Proto-Indo-European term to only refer to the members of a species belonging to a specific gender.