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English definition of “spy on sb/sth”

spy on sb/sth

phrasal verb with spy     /spaɪ/ verb
C2 to watch someone or something secretly , often in order to discover information about them or it: He was spying on her through the keyhole .Spying and espionage
(Definition of spy on sb/sth from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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