The Collaborative International Dictionary of English v.0.48:

Hagioscope \Ha"gi*o*scope`\ (h[=a]"j[i^]*[-o]*sk[=o]p`), n. [Gr.
   "a`gios sacred + -scope.]
   An opening made in the interior walls of a cruciform church
   to afford a view of the altar to those in the transepts; --
   called, in architecture, a squint. --Hook.
   [1913 Webster] hag-ridden