Wiktionary
n. A slit, as in a castle wall, through which arrows can be fired.
Wikipedia
An arrowslit (often also referred to as an arrow loop, loophole or loop hole, and sometimes a balistraria) is a thin vertical aperture in a fortification through which an archer can launch arrows.
The interior walls behind an arrow loop are often cut away at an oblique angle so that the archer has a wide field of view and field of fire. Arrow slits come in a remarkable variety. A common and recognizable form is the cross. The thin vertical aperture permits the archer large degrees of freedom to vary the elevation and direction of his bowshot but makes it difficult for attackers to harm the archer since there is only a small target at which to aim.
Balistraria can often be found in the curtain walls of medieval battlements beneath the crenellations.
Usage examples of "arrowslit".
Serafelle was intently reading an old book with a worn, faded leather cover, handling its tattered pages carefully, while plump Verin, sitting cross-legged beneath an arrowslit, held a small blossom up to the light and made notes and sketches in a precise hand in a book balanced on her knee.
Rubbing her arms, the Amyrlin Seat walked over to peer through the narrow arrowslit at the garden below.
A bluefinch perched in an arrowslit like a mockery of her weather sense, peering into the hallway.
Nynaeve dashed to the nearest arrowslit and peered down at the outer courtyard.
Pulling it back, he took from the arrowslit window it covered a jar of wine, now cooled by the frigid outdoor temperature.
Abruptly, the light flicked out and the entire tower was dark, except for one arrowslit on the level above the one where her own room was.
It was not a big room, and its windows, a pair of tall, narrow arrowslits looking down on one of the inner courtyards, did nothing to make it seem larger.
A peal of trumpets rolled through the arrowslits, trumpets calling the fanfare from outside the walls, trumpets answering from the keep towers.
Brocaded curtains sided the tall arrowslits to make them seem more like windows.
Beyond the arrowslits, darkness grew and pressed on the light from the lamps in the corridor.
Sunlight streamed through the arrowslits, painting the bare stone walls.
The curtains had been partially drawn over the arrowslits, but the gaps let in enough light behind her to make her face hard to see clearly.
There were no windows but arrowslits, the tower top was deeply crenellated, and the door was of iron a foot thick, judging by the fact that it had not rusted away in all the intervening years.
Instantly haloes of strange color glimmered around the arrowslits and braziers.
Between the tapestries, arrowslits pierced the walls high up, angled to cover the corridors in both directions, and no flight of sweeping stairs but had arrowslits placed so the staircase could be swept by arrows or crossbow bolts.