The Collaborative International Dictionary of English v.0.48:
Peephole \Peep"hole`\, n. A hole, or crevice, through which one may peep without being discovered. [1913 Webster]WordNet (r) 3.0 (2006):
peephole n 1: a hole (in a door or an oven etc) through which you can peep [syn: peephole, spyhole, eyehole]