An Etymological Dictionary of the German Language/zwang
zwang, m., ‘compulsion, force, restraint,’ from MidHG. twanc, zwanc (g), m., ‘compulsion, distress, oppression’ (comp. MidHG. des lîbes twanc, ‘tenesmus, constipation’), OHG. dwang (gidwang), m., ‘distress, contraction, compulsion’; abstract of zwingen. Allied to zwängen, vb., ‘to squeeze, constrain, force,’ denomin. of Zwang, MidHG. twęngen, ‘to use violence to, squeeze in, oppress,’ OHG. dwęngen, ‘to use violence to’ (OHG. and MidHG. zwangen, zwęngen, ‘to pinch’; comp. MidHG. zwange, ‘tongs’); see also zwingen. A Teut. root þwenh (Aryan twenk) is implied by OHG. dûhen, Du. duwen, AS. þŷan, ‘to press, oppress’ (from *þunhjan).