An Etymological Dictionary of the German Language/Kreuz
Kreuz, n., ‘cross,’ from the equiv. MidHG. kriuz, kriuze, n., OHG. chrûzi, n.; from Lat. crŭci- (dat. cruci, acc. crucem), with change of vowel quantity in the stem as in Leier, Lilie, and Litze, and also of gender (comp. Abt, Orden, and Pech). The change of medial c in the Lat. word to HG. tz, though in another group of (older) loan-words Lat. c, even before open vowels, appears as k in HG. and Teut., is due to the fact that words like Keller and Kaiser were introduced into Germany at a far earlier period than Kreuz, which was adopted with Christianity in the 8th and 9th cents. The Goths used Teut. Galgen (Goth. galga), the English of the earliest period, rood (comp. Rute). The loanword is now found in all the Mod. Teut. languages — Ic. kross, Swed. and Dan. kors, Du. kruis, E. cross.