Meaning & use
spy on
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Meanings
verbphrasal verb
To watch or listen to someone secretly in order to learn what they are doing or saying.
Grammar: The object always follows on: she spied on her neighbors, not she spied her neighbors.
Patterns
- spy on someone
- spy on someone doing something
He was caught spying on his coworkers through the office window.
The children crept to the stairs to spy on the party below.
Some apps spy on users by tracking their location.
verbphrasal verb
To gather secret information about a country, company or group on behalf of another government or organization.
Grammar: The object is the target: agents spy on foreign governments.
Patterns
- spy on a country
- be accused of spying on someone
The embassy official was accused of spying on the host country.
Rival firms have been known to spy on each other's research.
Intelligence agencies spy on suspected terrorists.
Word forms
| third person singular | spies on |
|---|---|
| past tense | spied on |
| past participle | spied on |
| -ing form | spying on |
Common combinations
- spy on your neighbors
- She spied on her neighbors from behind the curtain.
- accused of spying on
- The firm was accused of spying on its employees.
- spy on someone's phone
- Stalkerware lets people spy on someone's phone.
- secretly spy on
- He secretly spied on his sister's diary.
- caught spying on
- The student was caught spying on the exam room.
Synonyms and how they differ
- watch
- Watch is neutral and does not suggest secrecy or wrongdoing the way spy on does.
- snoop on
- Snoop on is more informal and suggests nosy curiosity rather than serious intelligence work.
- surveil
- Surveil is a formal verb used mainly for official monitoring by police or governments.
- eavesdrop on
- Eavesdrop on refers specifically to listening in, while spy on also covers watching.
Opposites
Word family
Commonly confused: spy on or spy?
spy on vs spy
Spy alone can mean to notice something suddenly, as in I spied a rare bird; spy on means to watch secretly.
Practice
The detective claimed that his rival had been _____ him for weeks.
Choose one answer.
The phrasal verb is spy on someone. The other prepositions are not used with this meaning.
Make it your own
Write a sentence using “spy on”, then check it and compare it with the examples above.