peephole[noun]Synonyms: spyhole, aperture, chink, crack, hole, opening
[TahlilGaran] English Synonym Dictionary ▲
peep‧hole /ˈpiːphəʊl $ -hoʊl/
noun [countable] a small hole in a door or wall that you can see through ⇒
spy hole [TahlilGaran] Dictionary of Contemporary English ▲