'Spook' definitions:

Definition of 'spook'

noun

Someone unpleasantly strange or eccentric [syn: creep, weirdo, weirdie, weirdy, spook]

noun

A mental representation of some haunting experience; "he looked like he had seen a ghost"; "it aroused specters from his past" [syn: ghost, shade, spook, wraith, specter, spectre]

verb

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

Definition of 'Spook'

From: GCIDE

Spook \Spook\ (sp[=oo]k), n. [D. spook; akin to G. spuk, Sw. sp["o]ke, Dan. sp["o]gelse a specter, sp["o]ge to play, sport, joke, sp["o]g a play, joke.]
1. A spirit; a ghost; an apparition; a hobgoblin. [Written also spuke.] --Ld. Lytton. [1913 Webster]
2. (Zool.) The chimaera. [1913 Webster]

Synonyms of 'spook'

From: Moby Thesaurus

affright,
agent,
agitate,
alarm,
apparition,
appearance,
astral,
astral spirit,
awe,
banshee,
bogey,
bug,
case,
character,
control,
convulse,
curdle the blood,
departed spirit,
discompose,
disembodied spirit,
disquiet,
distract,
disturb,
duck,
duppy,
dybbuk,
eidolon,
embroil,
form,
fright,
frighten,
funk,
ghost,
grateful dead,
guide,
hant,
haunt,
horripilate,
idolum,
immateriality,
incorporeal,
incorporeal being,
incorporeity,
larva,
lemures,
make one tremble,
manes,
Masan,
materialization,
obsess,
oddball,
oddity,
oni,
original,
perturb,
phantasm,
phantasma,
phantom,
poltergeist,
possess,
presence,
psych,
quiz,
raise apprehensions,
revenant,
scare,
shade,
shadow,
shake,
shape,
shrouded spirit,
specter,
spectral ghost,
spirit,
sprite,
spy,
stagger,
startle,
terrify,
terrorize,
theophany,
throw,
throw into confusion,
trouble,
undercover man,
unman,
unnerve,
unsettle,
unstring,
unsubstantiality,
upset,
vision,
walking dead man,
wandering soul,
wraith,
zombie