The present paper discusses evidence supporting the claim that the common Xinguan Arawak noun for ‘hand’, *wɨʂɨku, is a shared lexical innovation of this subgroup and that, in addition, a formation for ‘finger’ derived from a nominal compound with the roots for ‘hand’ and ‘head’, *kapɨ-tɨwɨ, sets Waurá, Mehinaku and Kustenaú apart from other languages of the family, including Yawalapiti. The reconstructed Proto-Arawak etymon for ‘hand’, *kʰapɨ, is preserved in the Xinguan Arawak languages only in the form of obscure cognates, instantiating interesting developments in lexical semantics as well as a relatively uncommon sound change in Yawalapiti. The discussion incorporates and addresses the historical linguistic significance of the earliest documentation of the Xinguan Arawak languages, the material gathered by Karl von den Steinen in 1887-1888. The analyses and data discussed highlight serious shortcomings in some of the reconstructed forms and diachronic developments advanced by Payne (1991), such as the postulation of a shift *a > ɨ in Waurá and the reconstruction of syllable-final *h for the Proto-Arawak language, one of the most controversial aspects of his comparative study.