eavesdrop

Short definition from Wiktionary

Verb

1. 1
   To hear (intentionally) a conversation one is not intended to hear; to listen in.
2. 2
   To listen for another organism's calls, so as to exploit them.

Noun

1. 1
   The dripping of rain from the eaves of a house.
2. 2
   The space around a house on which such water drips.
3. 3
   A concealed aperture through which an occupant of a building can surreptitiously listen to people talking at an entrance to the building.
4. 4
   The act of intentionally hearing a conversation not intended to be heard.