köken: From Middle High German tamm. Probably via Old High German *tamm from Proto-Germanic *dammaz, though it is sometimes considered a later back-formation from the verb dämmen. The modern consonantism is Central and Low German (compare Middle Low German dam).
köken: Inherited from Middle French digue, from Old French dike, diic, from Middle Dutch dijc (compare modern Dutch dijk), from Old Dutch diic, dīc, from Frankish *dīk, from Proto-Germanic *dīkaz (“pool”), from Proto-Indo-European *dʰeygʷ- (“to stick, stab, pierce, dig”). More at dig, dike, ditch.