An Etymological Dictionary of the German Language/Krieg
Krieg, m., ‘war,’ from MidHG. kriec(g), m., ‘exertion, endeavour to obtain something,’ then also ‘opposition, resistance, argument, discord, combat.’ The predominant meaning in ModHG. is the latest and ‘counter-effort' the earliest; comp. MidHG. einkriege, adj., ‘self-willed.’ For a similar evolution of meaning comp. OHG. flîȥ, ‘exertion, zeal, quarrel'; see Fleiß. The word is almost entirely unknown to OHG.; it occurs once as chrêg, ‘pertinacia,’ with which widarkrêgi, ‘controversia', widarkriegelîn, ‘obstinatus’ (with obscure ê, ia, ie), are connected. This word, obscure in origin, is shared only by Du. (krijg) with G.; in all the other Teut. languages it is wanting, Dan. and Swed. krig being borrowed from G. Comp. the following word.