An Etymological Dictionary of the German Language/Schelm
Schelm, m., ‘rogue, knave, villain,’ from MidHG. schęlme, m., ‘pest, plague; those who have fallen in battle,’ then, as an abusive term, ‘wretch, seducer,’ OHG. scalmo, scęlmo, ‘plague.’ In MidDu. and MidLG. schelm has the old sense of ‘carrion, cadaver,’ so too in Bav. For the development of the meaning ‘rogue’ from ‘wretch,’ comp. Schalf, which has also acquired a milder signification. From the ModHG. word are derived Du. schelm and Ic. skelmir, ‘rogue.’