From Longman Dictionary of Contemporary Englishpeepholepeep‧hole /ˈpiːphəʊl $ -hoʊl/ noun [countable] SYLOOK ATa small hole in a door or wall that you can see through → spy hole
Examples from the Corpus
peephole• At 12: 14 a. m., there was a knock from inside the chamber and a peephole slid open.• I told him the history of the charts, my initial idea for a peephole of some sort.• Although it is sometimes simulated by looking through a peephole, this gives only a crude approximation of the condition.• He wiped a peephole from the condensation on the window and viewed the world beyond.• Al Capone and bootleggers filled the vacuum: bathtub spirits, peepholes in the door, Joe-sent-me.• The astonished researchers worked out the number of such peepholes in the sky, and did the sums.• He puts his selected objects into lighted cases and projects their images outward through lenses in the peepholes.• The tiny peephole let in some light, not enough to be distracting. 