An Etymological Dictionary of the German Language/Annotated/Enkel
Enkel (1.), masculine, ‘ankle,’ from Middle High German ęnkel, masculine, Old High German ęnckil, anchal, masculine; numerous primitive variants obscure the etymology. Old Icelandic ǫkkla, neuter, Anglo-Saxon ǫncleów, neuter (English ankle), Middle Dutch anclau, Old High German anchlâo, ‘anklebone,’ seem to be modifications of the primary form, but do they suggest any connection with Klaue (compare Anglo-Saxon ondcleów with oncleów)?. There is a difficulty in determining the relation of Old High German ęnchil, anchal, to anchlâo, and their further connection with Middle High German anke, masculine, ‘joint of the foot, nape’ (even now Anke in Upper German and Middle German dialects is the term for ‘nape, neck’), Old High German ęncha, feminine (from ankia), ‘thigh, tibia’ (French anche, ‘reed, mouthpiece’). Perhaps allied to Sanscrit án̄ga, ‘limb,’ an̄gúri, ‘finger.’
Enkel (2.), masculine, from the equivalent Middle High German ęnenkel, ęninkel, masculine, late Old High German ęninchilî(n), neuter, ‘grandson.’ Since even in Middle High German the forms ęnikel and ęniklîn appear, Modern High German 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; compare Anglo-Saxon scipincel, ‘small ship,’ liþincel, ‘small limb,’ Old High German lęwinchilî(n), ‘small lion,’ huoninchilî(n), ‘chicken.’ Hence Old High German ęninchilî is a diminutive of Ahn, Old High German ano (Gothic *ana, genitive *anin-s), ‘grandfather,’ and signifies literally ‘little grandfather, grandfather's child’; compare the similar evolution of meaning in Latin avunculus (see Oheim). In the non-Teutonic languages there is probably another corresponding term besides the word cited under Ahn — Old Slovenian vŭnukŭ, ‘grandson.’