supergrass

The trial collapsed when the main witness turned out to be a supergrass who had implicated dozens of gang members.

用法提示：supergrass 作名词，指供出多名罪犯的警方线人。

Detectives often rely on a supergrass to provide evidence against the whole network.

用法提示：supergrass 作名词，在短语 rely on 后作宾语，指警方线人。

He agreed to become a supergrass and named twenty former associates in court.

用法提示：supergrass 作名词，作 become 的表语，表示告密者的身份。