WordWeb Online

1. Watch, observe, or inquire secretly
   - stag, snoop, sleuth
    
2. Catch sight of; to perceive with the eyes
   "he caught spy of the king's men coming over the ridge";
   - sight, descry, spot, espy
    
3. Secretly collect sensitive or classified information; engage in espionage
   "spy for the Russians"

1. (military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors
   - undercover agent
    
2. A secret watcher; someone who secretly watches other people
   "my spies tell me that you had a good time last night"
    
3. A person secretly employed in espionage for a government
   - secret agent, intelligence officer, intelligence agent, operative, spook [informal]

Derived forms: spied, spies, spying

Type of: agent, comprehend, enquire [Brit, Cdn], inquire, investigate, looker, monitor, perceive, spectator, supervise, viewer, watchdog, watcher, witness

Encyclopedia: Spy, Counterspy