An Etymological Dictionary of the German Language/Annotated/Mönch
Mönch, masculine, ‘monk, friar,’ from the equivalent Middle High German münch, münech, Old High German munih (hh), masculine. From the primary form muniko-, monico-, the equivalent French moine is also derived. In the original Latin word monachus (μοναχός), ‘monk,’ the ch was probably pronounced as c; compare Italian monaco, Old Irish manach, Anglo-Saxon munuc, English monk; so that Old High German ch is the High German permutation of k. In that case Mönch was borrowed at an earlier period than Abt and Pabst (see Münster). Old Slovenian mŭnichŭ is a German loanword.