- Proto-Sino-Tibetan: ?
- Proto-Tibeto-Burman: *s/m/g/-rus (Matisoff, STEDT); *rus (Weidert, 1987 TBTo; Michailovsky, 1991 Kr; LaPolla, 1987; Benedict, 1972 STC)
A Chinese reflex appears to be lacking. Chinese 骨 (gŭ < OC *kˁut, "bone") is sometimes compared with this root. Although Lepcha a-hrǎt ("bone") and Karen k(h)rut ("bone") show a final -t, the correspondence is still problematic as there is no medial *-r- in the Chinese word. Interestingly, there is a Chinese cognate to Written Tibetan rus ("clan"): 類 (lèi < OC *rut-s, "category, clan"); note that the sense "clan" is likely a secondary derivation from "bone" > "lineage, family". Compare also Chinese 骸 (hái < OC *ɡˁrə, "bones, skeleton") and 頄 (kuí < OC *ɡʷru, "cheekbone").