An Etymological Dictionary of the German Language/trennen

by Friedrich Kluge

trennen, vb., ‘to separate, sever,’ from MidHG. and OHG. tręnnen (older *trannjan), wk. vb., ‘to split, separate, cleave,’ lit. ‘to partition off’; factitive of MidHG. trinnen, ‘to run away, separate’ (comp. abtrünnig). This verbal stem is unknown to the other Teut. languages, and hence its primit. Teut. and pre-Teut. form and meaning cannot be ascertained.