eavesdrop

What it means

1. ambitransitiveTo hear (intentionally) 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.

   1 more example

   You shouldn't eavesdrop, David. I told you: You'll only hear things you'll wish you hadn't.

   1999 February 3, Anthony Horowitz et al., “Strangler's Wood”, in Midsomer Murders

2. biologyTo 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

   1 more example

   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

In a sentence

I hope nobody was eavesdropping on our conversation last night, since it got so personal.

Where it comes from

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