Hagioscope

Squint in wall of north aisle chapel, St Nicholas's Church, Walcot, Lincolnshire, looking towards south-east, with a view of the high altar in the chancel beyond. To its right is a piscina supported by a carving of a man's head on the jamb of the wall.
The squint at the Church of the Blessed Virgin Mary, Compton Pauncefoot, Somerset

A hagioscope (from Ancient Greek άγιος (ágios) 'holy' and σκοπεῖν (skopeîn) 'to see') or squint is an architectural term denoting a small splayed opening or tunnel at seated eye-level, through an internal masonry dividing wall of a church in an oblique direction (south-east or north-east), giving worshippers a view of the altar and therefore of the elevation of the host.[1] Where worshippers were separated from the high altar not by a solid wall of masonry but by a transparent parclose screen, a hagioscope was not required as a good view of the high altar was available to all within the sectioned-off area concerned. Where a squint was made in an external wall so that lepers and other non-desirables could see the service without coming into contact with the rest of the populace, they are termed leper windows or lychnoscopes.

  1. ^  One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Hagioscope". Encyclopædia Britannica. Vol. 12 (11th ed.). Cambridge University Press. p. 817.