a person who listens to someone's private conversation without them knowing

Doris mouthed the words, looking towards the door for fear of eavesdroppers. 多丽丝一边说着，一边看向门口，生怕有人偷听。

The country's cellular networks are vulnerable to eavesdroppers. 该国的移动电话网络很容易被窃听者侵入。