An Etymological Dictionary of the German Language/Annotated/schmunzeln

by Friedrich Kluge

schmunzeln, verb, ‘to smile good-naturedly, simper,’ frequentative of Middle High German smutzen, smotzen, ‘to smirk, smile good-naturedly,’ to which Middle High German smutz, Modern High German (dialectic) Schmutz, ‘kiss,’ is also probably allied. It is perhaps connected with Schmatz, schmatzen (from Middle High German smackezen).