periscope
n.n. a tool that lets you see around a corner or over a wall. It is made of two mirrors that reflect light so you can see things that are hidden from your view.
n. an optical instrument consisting of a pair of mirrors set at an angle to each other, allowing the viewer to see around corners or over obstacles. Often used in military contexts or for simple observation in tight spaces.
He used a periscope to look around the corner of the building.
The soldiers used a periscope to observe the enemy camp without exposing themselves to direct fire.
In the absence of modern surveillance technology, the periscope served as a vital tool for reconnaissance, providing a clear line of sight through narrow alleyways and high walls.
Formed in English from peri- + -scope.