dudum

From Proto-Italic *dūdom, from base *dū, of unclear origin. De Vaan suggests it is related to dūrus, from PIE *dweh₂- (“far, long”), and therefore cognate with Ancient Greek δήν (dḗn, “for a long time, long ago”) and Proto-Slavic *davě (“long ago”) (whence *davьnъ (“ancient”)). Per Lewis and Short, from diū + dum.