squint
n.a small opening or hole in a wall, especially one that is small enough to see through but not to walk through. It is often used to let light into a building or to see what is happening outside.
n.a small opening in a wall, typically designed to admit light or provide a view. Often used in architectural contexts to describe narrow apertures in thick masonry.
“The old castle has a small squint in the thick stone wall.”
“Light streamed through the narrow squint, illuminating the dark corners of the medieval chapel without allowing rain to enter.”
“Architects often incorporate a squint into the design of a fortress to allow defenders to observe the surrounding landscape while remaining protected from direct fire.”
“So I squinted a bit and tried to imagine my son in that room, which is when it hit me: he’s actually serious about this.”
Derived from asquint (“obliquely, with a sidelong glance”).
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.