An Etymological Dictionary of the German Language/Annotated/Keil

by Friedrich Kluge

Keil, masculine, ‘wedge, keystone,’ from Middle High German kîl, ‘wedge, plug,’ with the curious variant kîdel (Modern High German dialectic Keidel), Old High German chîl, ‘plug’; both the Middle High German forms assume Gothic *keiþls’. Scandinavian keiler (Gothic *kaileis), masculine, ‘wedge,’ is abnormal; the root is kî, kai. Old Icelandic kill, ‘canal’ (compare the proper name Kiel), is probably not connected on account of the meaning; since Old High German and Middle High German kîl signifies ‘plug,’ the word is more probably allied to Anglo-Saxon cœ̂g, English key.