Spook
/spuːk/noun
A ghost or apparition; informally, a spy or intelligence agent.
Did you know?The intelligence-agent sense emerged in American English during the early 20th century, likely because spies were imagined as unseen, secretive figures—literal human “ghosts.”
Etymological Timeline
Middle Dutch
Middle Dutch
spooc
“A ghost, apparition, or specter”
16th–17th Century
Dutch
spook
“A ghost or frightening apparition”
18th Century
Pennsylvania German / American usage
spook
“A ghost; a supernatural apparition”
Early 19th Century
American English
spook
“A ghost or frightening person”
Early 20th Century
American English
spook
“A spy or intelligence agent, especially one operating secretly”
Modern English
English
spook
“A ghost, or informally a spy or intelligence operative”