An Etymological Dictionary of the German Language/Annotated/Zaum
Zaum, masculine, ‘bridle, rein,’ from the equivalent Middle High German and Old High German zoum, masculine; corresponding to Old Saxon tôm, Dutch toom, Old Icelandic taumr, ‘bridle, rein.’ The meaning makes it probable that the word is derived from the Teutonic root tug, tuh, ‘to draw’ (taumo- for *taugmo-, Aryan doukmo-; compare Traum); hence Zaum is literally ‘drawing strap.’