eavesdrop

Etymology

eaves + drop; the "listening" sense derives from the notion of the listener standing in the area denoted by the physical sense.

verb

1. (transitive, intransitive) To hear a conversation one is not intended to hear; to listen in.
   I hope nobody was eavesdropping on our conversation last night, since it got so personal.
2. (zoology) To listen for another organism's calls, so as to exploit them.
   […] Eastern Red Bat will eavesdrop on the sonar calls of other red bats to locate potential insect prey. 1993, David W. Nagorsen, Robert Mark Brigham, Royal British Columbia Museum, Bats of British Columbia, page 109
   Frog-biting midges also depend on eavesdropping for reproduction, and one would predict similarly strong selection to evolve auditory adaptations for hearing and localizing calls of their hosts. 2014, Ken Yasukawa, Animal Behavior: How and Why Animals Do the Things They Do

noun

1. The dripping of rain from the eaves of a house.
2. The space around a house on which such water drips.
3. (countable) A concealed aperture through which an occupant of a building can surreptitiously listen to people talking at an entrance to the building.
4. (countable) The act of intentionally hearing a conversation not intended to be heard.
   Were you having a little eavesdrop on us last night?