WordNet (r) 3.0 (2006):

spooky
    adj 1: unpredictably excitable (especially of horses) [syn:
           skittish, flighty, spooky, nervous]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "spooky":
   creepy, eerie, eldritch, fidgety, ghost-haunted, ghost-ridden,
   goosey, haunted, high-strung, jittery, jumpy, macabre, nervy,
   obsessed, ominous, possessed, specter-haunted, spirit-haunted,
   spooked, spookish, twittery, uncanny, unco, uncolike, unearthly,
   unrestful, weird