noun
rear gunsight having an open notch instead of a peephole or telescope
* * *
noun : a firearm rear sight having an open notch instead of a peephole or a telescope
* * *
(on a firearm) a rear sight consisting of a notch across which the gunner aligns the front sight on the target. Cf. peep sight.
[1585-95]
* * *
open sight,
a rear sight on rifles, shotguns, and other weapons, consisting of a small metal plate with a V-shaped notch through which the front sight and target are brought into alignment.
Useful english dictionary. 2012.