An Etymological Dictionary of the German Language/Boot
Boot, n. ‘boat,’ ModHG. only (not found in Luther), borrowed from LG. boot; comp. the equiv. Du. boot, AS. bât, E. boat, OIc. beitr. This word, which is still unknown to the UpG. dialects, is at all events native to England, whence it made its way during the AS. period into OIc. (bátr), and in MidE. times to the Continent (Du. boot). The origin of AS. bât, OIc. beitr, has not been discovered; like many other nautical terms, this word too is first recorded in Eng. Moreover, the assumption that the word was borrowed in primit. Teut. times must be discarded.