eaves·drop 
/ˈivzˌdrɑ:p/ verb
eaves·drops; eaves·dropped; eaves·drop·ping /ˈivzˌdrɑ:p/ verb [no obj] : to listen secretly to what other people are saying — usually + on ▪ He was eavesdropping [=listening in] on his sister and her friends in the next room. ▪ She was accused of eavesdropping on private telephone conversations.
— eaves·drop·per noun, plural eaves·drop·pers [count]
— eavesdropping noun [noncount]
▪ electronic eavesdropping
▪ electronic eavesdropping
