Cognates are found in every branch of Volta-Niger, with languages adopting the definition of hand, arm, or both, and most branches of Volta-Congo. Westerman reconstructs the term as "arm" to Proto-Atlantic-Congo *-bua-. The root term, *ɓɔ́ is cognate with Proto-Edoid *ɓɔ, Proto-Idomoid *-bwɔ, Proto-Igboid *bɔ̀, Proto-Gbe *-bɔ́, Proto-Ebiroid *ʊ-bɔ, Proto Arigidi *wɔ́, Akpes ɔbɔ, and Oko-Eni-Osayen úbá
Cognates can also be found in more distantly-related Benue-Congo proto-languages including Proto-Ukaan *ʊ̀wɔ́, Proto-Lower Cross River *ú-bɔk, Proto-Ogoni *ɔ̀bɔ́, and several reconstructed Proto-Plateau terms, Proto-Plateau *-bwak (Kagoro), Proto-Plateau *gu-bok (Jaba), and Proto-Plateau *-bwak (Beromic), see Proto-Benue-Congo *-boko. Also see cognates among Gur languages, Proto-Oti-Volta *ba, Proto-Eastern Oti-Volta *ba-, Proto-Grassfields *bó, perhaps related to Akan abasa, and maybe even Proto-Ijoid *ɓara. All this suggests a much older inheritance[1] , the Proto-Yoruboid term is proposed to derive from Proto-Volta-Niger *ɔ́-bɔ́, with a common Proto-Volta-Congo source, see another proposed reconstruction to Niger-Congo. Proto-Niger-Congo *-bo [2]
The other reconstructed Niger-Congo root *ka (“hand”) can be seen in Proto-Yoruboid *á-ká
*ɔ́-ɓɔ́