From Longman Dictionary of Contemporary Englishspyholespy‧hole /ˈspaɪhəʊl $ -hoʊl/ noun [countable] British English a hole in a door, wall etc, through which you can look at someone secretly
Examples from the Corpus
spyhole• Amin crossed to the other side of the chamber and looked through a spyhole in the wall.• There was a spyhole in one of the flats.• She acknowledged the spyhole and peered through it, sometimes, when the sleeplessness got very bad.• He raised his head a moment and looked directly at the spyhole as if he sensed some one watching.• The guard slid the cover off the spyhole on the door.• Yet if she moved the chair, she saw the spyhole.• Contrary to her usual habit she did not glance through the spyhole before beginning to undo the chain.• Then a little light came through the uncovered spyhole, a flickering, surreptitious light. 