Definition: a spy who makes uninvited inquiries into the private affairs of others
Similar words: spy
Definition: a secret watcher; someone who secretly watches other people
Usage: my spies tell me that you had a good time last night
Synonyms: spy, stag, sleuth, snoop
Definition: watch, observe, or inquire secretly
Similar words: monitor, supervise
Definition: keep tabs on; keep an eye on; keep under surveillance
Usage: we are monitoring the air quality; the police monitor the suspect's moves