Definition of "spy on" []

• To secretly watch; to surveil. (verb)

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• "The Nova Group had used her to spy on NTAC during the “Vesuvius Affair.”"
• "Young Partin had been sent to spy on me that night, and that could have happened only if Sparacino knew I was there with Mark."
• "After all, as I know from one of her stories, she was summoned to the Ivanovo NKVD headquarters after the war, after her uncle Volya had already been arrested and shot, and forced to spy on the chairman of the anatomy department where she worked."