An Etymological Dictionary of the German Language/Annotated/Unflat
Unflat, masculine, ‘filth, dirt,’ from Middle High German un-vlât, masculine, neuter, and feminine, ‘dirtiness, untidiness’; to which is allied unflätig, adjective ‘filthy, nasty,’ from Middle High German unvlœtic, ‘unclean, untidy.’ Old High German *flât, ‘beauty,’ is met with only in female proper names (Sigi-, Muot-, Hruoī̆-flât). The early history of Old High German *flât (Gothic flêd, Anglo-Saxon flœ̂d in proper names) is obscure.