An Etymological Dictionary of the German Language/Annotated/Tonne
Tonne, feminine, ‘tun, cask, barrel,’ from the equivalent Middle High German tunne, Old High German tunna, feminine. A corresponding word with a similar form is preserved by Dutch ton, Anglo-Saxon tunne, English tun; according to these Low German cognates the High German word ought to have an initial z, or rather the cognates an initial d. Hence the word must have been borrowed by one or the other, which is all the more probable since it is wanting in Swabian and Bavarian. The Romance languages have French tonne (tonneau), Spanish and Portug. tonel. Probably Keltic is the ultimate source of the word; compare Irish and Gaelic tunna, ‘tun, cask.’ In that case, the word passed into High German after 700 A.D., When the t could not be permutated to z. The form of Old Swedish þyn, ‘tun, cask,’ shows that it was borrowed at a much earlier period.