From Middle High German verhelīn, from Old High German farhilī, farhilīn, diminutive of farah (“pig”), from Proto-Germanic *farhaz, whence English farrow.
The -k- has been explained as an irregular fortition of -h-, which would be plausible if the form were of Upper German origin, where -h- was strong and where there was dialectal variation between -rch- and -rk-. However, Middle High German verkelen is first found in West Central German along the Rhine, where stem-internal -h- had been lost early on (compare accordingly Middle High German verlīn). It therefore seems at least equally probable that the -k- is due to influence by a related Rhenish word for “pig, piglet”, still found today in Ripuarian Ferke, which goes back to a Frankish *far(i)kīn (compare Old Dutch farkīn, ferkīn, whence modern Dutch varken), from Proto-Germanic *farhikīną, another diminutive of *farhaz.
Ferkel n (strong, genitive Ferkels, plural Ferkel, diminutive Ferkelchen n or Ferklein n)