köken: Inherited from Old Ruthenian дво́йчи (dvójči), from Old East Slavic дъвоичи (dŭvoiči), from Proto-Slavic *dъvojьťi. Cognate with Belarusian дво́йчы (dvójčy), Old Polish dwójcy. By surface analysis, дві (dvi) + -чі (-či).
From Old Latin duis (mentioned by Cicero), from Proto-Italic *dwis, from Proto-Indo-European *dwís (“in two, twice, doubly”), adverb derived from *dwóh₁ (“two”); compare Ancient Greek δίς (dís), Sanskrit द्विस् (dvís). Doublet of dis-.