An Etymological Dictionary of the German Language/Annotated/zufrieden
zufrieden, adverb and adjective, ‘contented, satisfied,’ Modern High German only; originally only an adverb formed by the combination of the preposition zu and the dative of the substantive Friede. Hence the original meaning of zufrieden is ‘in peace, quietly, protection.’ In Middle High German mit vride (compare abhanden, behende) was the equivalent expression.