Definition of "Spy" :
noun: (military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors
noun: a secret watcher; someone who secretly watches other people
verb: secretly collect sensitive or classified information; engage in espionage
"Spy for the Russians."
verb: watch, observe, or inquire secretly
verb: catch sight of
verb: catch sight of; to perceive with the eyes