- Proto-Sino-Tibetan: *ngwjəɣ (Coblin, 1986)
- Proto-Tibeto-Burman: *ŋwa (Matisoff, STEDT; Benedict, 1972; Weidert, 1987; LaPolla, 1987); *ngwa(*B) (Coblin, 1986)
Compare Thai งัว (ngua) / วัว (wua, “bullock, cow”), Lao ງົວ (ngūa, “bullock, cow”). Because of the restricted geographic distribution of this Tai etymon, Benedict (1972) suspects Chinese to be a Tai loan, also Li (1976) concludes the Tai item is not a Chinese loan as it is not found in northern Tai dialects. The relationship between this PST root and the Tai comparanda remains unclear.
- Old Chinese: 牛 /*ŋʷə/ (B-S), /*ŋʷɯ/ (ZS) ("cattle")