An informer is a person who tells the police that someone has done something illegal.
例句
...two men suspected of being police informers.被怀疑是警方线人的两名男子
英汉词典释义
n.
间谍,情报人员
The service had planted its agents and informers in some key positions in industry.特工处已将特工和密探安插在工业部门的某些重要工作岗位上。One of the gang members had turned informer.团夥中的一员后来变成了告密者。The police provided a safe house for the informer.警方给线人提供了一个安全屋。
英英词典释义
Noun
1. one who reveals confidential information in return for money