EAVESDROP

v. listen in on another person's private conversation, snoop, spy

To eavesdrop is to surreptitiously overhear a private conversation.
See more at Wikipedia.org...

Verb
1. listen without the speaker's knowledge; "the jealous man was eavesdropping on his wife's conversations"
(synonym) listen in
(hypernym) listen
(hyponym) wiretap, tap, intercept, bug
(derivation) eavesdropper

(v. i.)
To stand under the eaves, near a window or at the door, of a house, to listen and learn what is said within doors; hence, to listen secretly to what is said in private.
  

(n.)
The water which falls in drops from the eaves of a house.
  

Synonyms and related words:
attend, attend to, auscultate, be all ears, bend an ear, bug, cock the ears, examine by ear, give attention, give audience to, give ear, hark, hear, hear out, hearken, heed, intercept, lend an ear, listen, listen at, listen in, listen to, overhear, pry, sit in on, snoop, spy, tap, wiretap