The Irish translation given on the OS map sheet 43 for Bellewstown is Baile an Bheileogaigh. Beile or bile is the name given to old inauguration trees. So the town of the inauguration tree of the Ogaigh’s (possibly another version of Haughey?)
However, on the western approach to the town is a sign that says Sliabh B.(aile) na gCailleach, the Hill of the town of the Hag.