眼線 Informant or Spy usually refers to someone acting as a secret source

Relation Nicknames

间谍 [jiān dié]
间谍 simply means Spy A spy refers to someone who secretly gathers information about another country ...
卧底 [wò dĭ]
Undercover usually refers to a spy or someone working undercover in criminal organizations or enemy ...
碟中谍 [dié zhōng dié]
Meaning Spy inside Spy derived from famous movie titles or plots involving espionage Likely indicates ...
刺探 [cì tàn]
Intrigue or Espionage A more literal sense could imply gathering secret information which may also ...