An Etymological Dictionary of the German Language/Annotated/jetzt
jetzt, av. (older ietz, like ie for je), ‘now, at the present time,’ from the equivalent Middle High German ietze, iezuo (hence the archaic Modern High German jetzo), beside which Middle High German iezunt, Modern High German jetzund, with a new suffix, occurs. How the adverb ie-zuo, recorded in earlier Middle High German, can mean ‘now’ is not clear; compare Middle High German iesâ, ‘at once,’ from ie (see je) and sâ, ‘at once.’