The spelling of the name ‘Healeyfield’ has taken many forms over the centuries, including Heleie, Heleya de sato, Elemos, and Heley Aleyn however the general consensus seems to be that all relate to an area of land that has been cleared or that is in a clearing. There is more than one explanation of the origin of the name of Castleside. The first tenant of a farmhouse built in the then Lanchester Parish in around 1773 was named ‘Castle’.
In addition the attached farmland was on the north side of the old Watergate-Stanifordham Road between the farm and the Lane Ends Inn, now the Horse and Groom Pub. The combination of these some say is the origin of Castleside. Another theory is that the area, now called Castleside, was the part of the original village, which was on the ‘castle’ side, and referred to the view of the castle-like ruin of Muggleswick Monastic Grange.