An Etymological Dictionary of the German Language/Annotated/trennen

by Friedrich Kluge

trennen, verb, ‘to separate, sever,’ from Middle High German and Old High German tręnnen (older *trannjan), weak verb, ‘to split, separate, cleave,’ literally ‘to partition off’; factitive of Middle High German trinnen, ‘to run away, separate’ (compare abtrünnig). This verbal stem is unknown to the other Teutonic languages, and hence its primitively Teutonic and pre-Teutonic form and meaning cannot be ascertained.