Read the dictionary definition of spy. All definitions for this word.
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
2. a secret watcher; someone who secretly watches other people
1. my spies tell me that you had a good time last night
3. secretly collect sensitive or classified information; engage in espionage
1. spy for the Russians
4. watch, observe, or inquire secretly
5. catch sight of
6. catch sight of; to perceive with the eyes
1. he caught sight of the king's men coming over the ridge