spook

Short definition from Wiktionary

Noun

1. 1
   A ghost or phantom.
2. 2
   A hobgoblin.
3. 3
   A scare or fright.
4. 4
   An undercover agent, spy, or intelligence analyst.
5. 5
   A black person.
6. 6
   A metaphysical manifestation; an artificial distinction or construct.
7. 7
   A psychiatrist.
8. 8
   A player who engages in hole carding by attempting to glimpse the dealer's hole card when the dealer checks under an ace or a 10 to see if a blackjack is present.

Verb

1. 1
   To frighten or make nervous (especially by startling).
2. 2
   To become frightened (by something startling).
3. 3
   To haunt.