An Etymological Dictionary of the German Language/Annotated/Bolz
Bolz, Bolzen, masculine, ‘short arrow-bolt,’ from the equivalent Middle High German bolz, Old High German bolz, masculine; compare the equivalent Old Icelandic bolte, Anglo-Saxon bolt, English bolt; allied to Dutch bout, ‘cramp-pin.’ The word has the same meaning in all dialects, and in all the various periods of the Teutonic languages. We may assume a pre-Teutonic bhḷdó-s, with the meaning ‘bolt, dart’; yet no such word outside the Teutonic group can be adduced. Bolzen cannot be immediately akin to Middle High German boln, ‘to throw, hurl,’ since the Teutonic t could not be explained as a derivative from pre-Teutonic d. But it is at least possible, on account of the great antiquity of the cognates, that they were borrowed from Latin catapulta and remodelled.