An Etymological Dictionary of the German Language/Annotated/Zwilling

by Friedrich Kluge

Zwilling, masculine, ‘twin,’ from the equivalent Middle High German zwinelinc, zwillinc (g), masculine (also zwiselinc and zwilich-kint), and zwinelîn, neuter, Old High German zwiniling, masculine. A derivative of the Old High German adjective, zwinal, ‘geminus, gemellus,’ and also, like zwinal, from zwi-, ‘twofold’; compare the equivalent English twin, Dutch tweeling, Danish tvilling.