1. A secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors
   "The spy infiltrated the criminal organization to gather evidence";
   - undercover agent
    
2. A person secretly employed in espionage for a government
   "The spy gathered crucial information about the enemy's plans";
   - secret agent, intelligence officer, intelligence agent, operative, spook [informal]
    
3. A secret watcher; someone who secretly watches other people
   "my spies tell me that you had a good time last night"

1. Secretly collect sensitive or classified information; engage in espionage
   "spy for the Russians"
    
2. Watch, observe, or inquire secretly
   "The detective spied around the suspect's house for clues";
   - stag, snoop, sleuth
    
3. Catch sight of; to perceive with the eyes
   "We spyd a ship on the horizon";
   - sight, descry [literary], spot, espy

Derived forms: spies, spied, spying

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

Encyclopedia: Spy, Counterspy