An Etymological Dictionary of the German Language/zufrieden
zufrieden, adv. and adj., ‘contented, satisfied,’ ModHG. only; originally only an adv. formed by the combination of the prep. zu and the dat. of the subst. Friede. Hence the orig. meaning of zufrieden is ‘in peace, quietly, protection.’ In MidHG. mit vride (comp. abhanden, behende) was the equiv. expression.