The window is of a design which is typical of a fourteenth century date, although it doesn't seem to fit in any of the window openings of the surviving building. They are from a plate tracery window which was designed to take glass. One of the stones has a small cross cut into its surface. This is either the mark of the mason, or possibly a mark to help the laying out of the window.
Several of the stones show signs of alterations, and it seems likely that the fourteenth century window was altered to make a casement window, before being removed when the building was modernised.