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