: an opening in the interior walls of a cruciform church so placed as to afford a view of the altar to those in the transept.

What is a squint in a church?

Hagioscope, also called squint, in architecture, any opening, usually oblique, cut through a wall or a pier in the chancel of a church to enable the congregation—in transepts or chapels, from which the altar would not otherwise be visible—to witness the elevation of the host (the eucharistic bread) during mass.

What is a leper hole?

A leper window was a window built low in the chancel wall of some medieval churches. It was usually iron barred and shuttered. Lepers stood outside and watched Mass through this window.