An Etymological Dictionary of the German Language/Annotated/Daumen

Daumen, masculine, ‘thumb,’ from the equivalent Middle High German and Middle Low German dûme, Old High German dûmo, masculine; compare Dutch duim, Anglo-Saxon þûma, English thumb; Old Icelandic þumall, þumalfingr. The same derivative with the suffix l is seen, but with a change of meaning, however, in Anglo-Saxon þŷmel, English thimble (Gothic *þûma). This word ‘thumb’ is consequently common to the Teutonic group; even the other fingers had each its special name in the Old Teutonic period. The Anglo-Saxon terms middefinger, midlesta finger, se goldfinger, se lîtla finger, are in complete accord with Modern High German Mittelfinger (middle-finger), Goldfinger (ring-finger), and der kleine Finger (the little-finger), respectively. These terms are not formed, therefore, like Daumen from an old independent stem; in this way Daumen is proved to be primitively, though etymologically it is not quite clear; the pre-Teutonic form may have been *tûmon, perhaps akin to tŭmeo, ‘to swell’?. In that case Daumen would be equivalent to ‘swollen finger’; compare also Sanscrit tumrá-s, as ‘greasy, fat, vigorous,’ and tûtuma-s, ‘strong,’ Zend tûma, ‘strong,’ with Latin tum-eo. Greek τυΐλος, τύλη(ū̆), ‘callosity, swelling, knob, hump,’ are based upon a root tū̆, while the Latin cognates point to tū̆m. The original sense of both may have been ‘to swell, be thick.’