n. A small opening in an interior wall of a church, enabling those in the transept to view the high altar; sometimes called a squint
the GNU version of the Collaborative International Dictionary of English
n. 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.
The Century Dictionary and Cyclopedia
n. In medieval architecture, an opening in a wall, screen, or barrier of a church, to afford a view of the chief altar to worshipers in the chapels or side aisles; a squint. See squint.
Word Usage
"In the west wall is a hagioscope, and from a room next the chapel a newel staircase led to the priest's room on the floor above."