A ghost or phantom.
The building was haunted by a couple of spooks.
A hobgoblin.
A scare or fright.
The big spider gave me a spook.
A spy.
A black person.
A metaphysical manifestation; an artificial distinction or construct.
He who is infatuated with Man leaves persons out of account so far as that infatuation extends, and floats in an ideal, sacred interest. Man, you see, is not a person, but an ideal, a spook. — Max Stirner
To frighten or make nervous (especially by startling).
The hunters were spooked when the black cat crossed their path. The movement in the bushes spooked the deer and they ran.
To become frightened (by something startling).
The deer spooked at the sound of the dogs.
To haunt.