peeking; peeping (e.g. through a hole, narrow gap)
peephole; spyhole; inspection hole; observation window
peephole (e.g. in a door); observation window; viewing window
peep show; device with lens mounted on a stand or in a box to view enlarged pictures; water glass; hydroscope; box, etc. with glass bottom for viewing underwater
peep show; device with lens mounted on a stand or in a box to view enlarged pictures
zoetrope (animation device)