0 a small hole in a door or a wall through which you can look, especially without being seen: --
1 a small hole in a door or a wall through which you can see to the other side --
Towers have limited access, contain few windows and many have narrow slots or peepholes placed in the walls.
Some stores have one-way mirrors to spy for the light-fingered and sometimes to catch the careless; there are the peepholes through the doors.
They are narrow cells with little peepholes in the doors, and the inmates are required to slop them out each morning.
The two peepholes assert the viewer is looking with both eyes, making the optical experience similar to looking into the illusory space of a stereoscope.
