# sleeper agent

CEFR C1 · Noun

Source: https://englishreference.com/word/sleeper-agent
Updated: 2026-07-28

## Definition

a spy who lives a normal life in another country for a long time. They do not do any spying until they are told to start their secret mission.

For teachers: an espionage operative who is placed in a target country or organisation not to conduct immediate operations, but to establish a deep-cover identity for future activation.

## Examples

- The sleeper agent lived as a quiet librarian for ten years.
- After living as a suburban father for a decade, the sleeper agent received a coded message to begin his mission.
- Intelligence agencies often struggle to identify the sleeper agent because their fabricated persona is indistinguishable from that of a law-abiding citizen with no suspicious connections.

## Usage notes

- Typically used in the context of espionage or political thrillers.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.