'Um Schlass' means at the castle.
Hesperange has had two castles. The ruin of the medieval castle, probably from the 13th century, stands 40 metres above the valley; Maximilian of Austria had it dismantled in 1480 and 1482. The old Urbéngs-Schlass made way in 1992 for the new town hall. We have not yet found out which of the two gave this housing estate its name.