An Etymological Dictionary of the German Language/Annotated/Kerl
Kerl, masculine, ‘fellow.’ a Middle German and Low German form for Middle High German karl, masculine, ‘man, husband, lover,’ Old High German karal; Old Icelandic karl, masculine, ‘man (opposed to woman), old man, one of the common folk, serf, servant,’ hence English carl, ‘fellow, man.’ Besides these terms, which indicate Gothic *karla-, there appears a form kerla- (Gothic *kaírla-) allied to them by gradation, and assumed by Anglo-Saxon čeorl, ‘serf’ hence čeorlian, ‘to take a husband, marry’), Middle English cheorl, English churl, as well as by Dutch kerel, Frisian tzerl, Low German kêrl, kerel (wanting in Old Saxon). As a proper name the High German Karl was retained without being supplanted by the Middle German and Low German form; on the adoption of Karl by Slavonic see under Kaiser. Both words denoted a full-grown man (generically, ‘husband, lover,’ and also ‘male of animals’ in Old High German and Anglo-Saxon; legally, ‘man of the lower orders’); in Anglo-Saxon 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-Teutonic cannot be adduced with any certainty; the comparison of kerl, karl, with Sanscrit jâra (j for g), ‘paramour, lover,’ is possible as far as the stem is concerned; the l of the Teutonic word is at all events a suffix. With regard to the gradation Kerl, Karl, compare Käfer, Giebel, Kiefer, Laut, &c.