An Etymological Dictionary of the German Language/Kerl
Kerl, m., ‘fellow.’ a MidG. and LG. form for MidHG. karl, m., ‘man, husband, lover,’ OHG. karal; OIc. karl, m., ‘man (opposed to woman), old man, one of the common folk, serf, servant,’ hence E. carl, ‘fellow, man.’ Besides these terms, which indicate Goth. *karla-, there appears a form kerla- (Goth. *kaírla-) allied to them by gradation, and assumed by AS. čeorl, ‘serf’ hence čeorlian, ‘to take a husband, marry’), MidE. cheorl, E. churl, as well as by Du. kerel, Fris. tzerl, LG. kêrl, kerel (wanting in OSax.). As a proper name the HG. Karl was retained without being supplanted by the MidG. and LG. form; on the adoption of Karl by Slav. see under Kaiser. Both words denoted a full-grown man (generically, ‘husband, lover,’ and also ‘male of animals’ in OHG. and AS.; legally, ‘man of the lower orders’); in AS. ceorl, ‘man,’ retained the entire signification, since it is used even of kings, and in the derivative ceorlian, ‘to marry,’ it preserves its generic meaning and its legal aspect in being applied to the common freemen and the serf. References in non-Teut. cannot be adduced with any certainty; the comparison of kerl, karl, with Sans. jâra (j for g), ‘paramour, lover,’ is possible as far as the stem is concerned; the l of the Teut. word is at all events a suffix. With regard to the gradation Kerl, Karl, comp. Käfer, Giebel, Kiefer, Laut, &c.