eavesdropper
/ˈivzˌdrɑpər/
noun
- A person who secretly listens to the private conversation of others.
- My little brother is such an eavesdropper; he always listens at my door.
- The spy was caught and accused of being an eavesdropper in the embassy.
- The eavesdropper hid behind the curtain to hear the secret plan.