Spook
Spook noun - A person who tries secretly to obtain information for one country in the territory of another usually unfriendly country.
Usage example: Russia recalled its spooks after the collapse of the Soviet Union
Sleeper and spook are semantically related. In some cases you can use "Sleeper" instead a noun "Spook".
Mutual synonyms
Cite this Source
Sleeper and Spook. (2016). Retrieved 2026, July 21, from https://thesaurus.plus/related/spook/sleeper
Spook & Sleeper. N.p., 2016. Web. 21 Jul. 2026. <https://thesaurus.plus/related/spook/sleeper>.
Sleeper or Spook. 2016. Accessed July 21, 2026. https://thesaurus.plus/related/spook/sleeper.
Google Ngram Viewer shows how "spook" and "sleeper" have occurred on timeline