spook

Definitions

Military

  • noun a person involved in extremely covert operations (e.g. spying, special forces, etc)

Slang

  • noun a black person. The reference is either an ironic one to the subjects’ black colour (as opposed to the white of spectres) or to their ‘haunting’ of certain locations.
  • noun a spy, secret agent. This usage may be a simple reference to unseen ‘ghosts’ or may derive from the fact that many World War II agents were recruited from the Yale secret society, the ‘Skull and Bones’.
http://www.dictionarycentral.com/definition/spook.html