An Etymological Dictionary of the German Language/Enkel
Enkel (1.), m., ‘ankle,’ from MidHG. ęnkel, m., OHG. ęnckil, anchal, m.; numerous primit. variants obscure the etymology. OIc. ǫkkla, n., AS. ǫncleów, n. (E. ankle), MidDu. anclau, OHG. anchlâo, ‘anklebone,’ seem to be modifications of the primary form, but do they suggest any connection with Klaue (comp. AS. ondcleów with oncleów)?. There is a difficulty in determining the relation of OHG. ęnchil, anchal, to anchlâo, and their further connection with MidHG. anke, m., ‘joint of the foot, nape’ (even now Anke in UpG. and MidG. dialects is the term for ‘nape, neck’), OHG. ęncha, f. (from ankia), ‘thigh, tibia’ (Fr. anche, ‘reed, mouthpiece’). Perhaps allied to Sans. án̄ga, ‘limb,’ an̄gúri, ‘finger.’
Enkel (2.), m., from the equiv. MidHG. ęnenkel, ęninkel, m., late OHG. ęninchilî(n), n., ‘grandson.’ Since even in MidHG. the forms ęnikel and ęniklîn appear, ModHG. Enkel is most closely connected with a form enekel, in which the medial e was syncopated. The termination inklîn is frequently found as a diminutive suffix; comp. AS. scipincel, ‘small ship,’ liþincel, ‘small limb,’ OHG. lęwinchilî(n), ‘small lion,’ huoninchilî(n), ‘chicken.’ Hence OHG. ęninchilî is a diminutive of Ahn, OHG. ano (Goth. *ana, gen. *anin-s), ‘grandfather,’ and signifies lit. ‘little grandfather, grandfather's child’; comp. the similar evolution of meaning in Lat. avunculus (see Oheim). In the non-Teut. languages there is probably another corresponding term besides the word cited under Ahn — OSlov. vŭnukŭ, ‘grandson.’