To secretly watch or gather information about a person or group
To secretly watch someone to find out what they are doing
2 meanings, ordered from most common to least. Color-coded by CEFR level.
To secretly watch a person or group in order to gather information about their activities
"The agency was accused of spying on its own citizens without legal authorisation."
The NSA has been spying on millions of ordinary Americans.
— Edward Snowden, interview with The Guardian, June 2013
To watch someone you know in a secretive and intrusive way out of jealousy, suspicion, or nosiness
"She caught her younger brother spying on her through the keyhole."
Always involves secrecy and is almost always considered negative or intrusive. Used in contexts ranging from governments and agencies to jealous partners and curious children. Common in news, politics, and spy fiction.
Natural word combinations native speakers use most often.
The five tense forms you'll use most often.
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