From Longman Dictionary of Contemporary Englishtwo-way mirrorˌtwo-way ˈmirror noun [countable] Dglass that is a mirror from one side, but that you can see through from the other
Examples from the Corpus
two-way mirror• Lifeline 1990 consists of a two-way mirror, paint, light, timers and wood.• It had been a short honeymoon: one night in front of a two-way mirror. 