An Etymological Dictionary of the German Language/Annotated/Schmerz
Schmerz, masculine, ‘pain,’ from the equivalent Middle High German smërz, masculine, Old High German smërzo, masculine, smërza, feminine; allied to Old High German smërzan, verb, Middle High German smërzen, ‘to smart, pain,’ Anglo-Saxon smeortan, ‘to pain, smart,’ English smart, verb and substantive Middle English smerte, English smart, adjective, make it probable that the cognates are related to Latin mordêre, ‘to bite,’ Greek σμερδνός, σμερδαλεός, ‘horrible'; the Aryan root smerd, Teutonic smert, signifies perhaps ‘to stick, bite.’ Compare bitter.