a person who gives secret information about somebody/something to the police or the media （向警方或报纸）提供消息的人，告密者， 线民 a police informant 警察线人 The journalist refused to reveal the identity of his informant. 记者拒绝透露其线人的身份。
- (specialist)
a person who gives somebody information about something, for example to help them with their research （为研究等）提供资料的人；合作者