An Etymological Dictionary of the German Language/Annotated/Eichel
Eichel, feminine, from the equivalent Middle High German eichel, Old High German eihhila, ‘acorn, fruit of the oak’ (corresponding to Dutch eikel). The form was originally a diminutive of Eiche, ‘the offspring of the oak,’ as it were; the derivative is wanting in English and Scandinavian. Eckern, Modern High German, is not a cognate. —