A spirit; a ghost; an apparition; a hobgoblin.

A spy, either from Naval Intelligence, CIA, National Security Agency or a nameless U.S. Navy organization that sends riders onboard to gather electronic intelligence when the ship is on a spec-op.

Generally accepted as an alternative term for "ghost", the origins of the word may be traced back to American Indian lore and thus regarded as a uniquely American term. In its purest sense, these spirits are regarded as benevolent and benign, capable of temporarily taking "possession" of a living body to perform good works. This type of ghost is sometimes said to be able to haunt a person without him/her ever being aware of it and can absorb themselves into the person at will. Along the Eastern United States, stories may be found in rural areas of men who were failures in life until their 'spook' took over them, enabling them to achieve wealth and success, as in the case of "walk-ins". The term has also come to describe intelligence operatives and government spies.

The chimæra.

Spook is an Australian band, comprising of Chanel Cole and Daniel Belle along with electronic producers Dennis Gascoigne and Leo Hede, better known as Statler & Waldorf.

frighten or scare, and often provoke into a violent action; "The noise spooked the horse"

A horse's reaction when startled.

a very, very shy dog

someone unpleasantly strange or eccentric

A fun 2D shoot-up side-scroller. Can be played either online or offline.

an internal security operative," Muldoon explained

attempting to glimpse the dealer's hole card.

An army signaller, especially a wireless operator. How this term came to be applied in this sense is doubtful although probably it was because the signaller at the instrument was able to receive messages apparently from space.

a person who infiltrates an organization and basically causes a change