The Collaborative International Dictionary of English v.0.48:

bloodcurdling \blood"curd*ling\ adj.
   causing sudden intense fear due to an apprehension of
   imminent bodily harm, to oneself or others. Awakened by a
   bloodcurdling scream from right outside her window

   Syn: hair-raising, nightmarish.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

bloodcurdling
    adj 1: extremely alarming [syn: bloodcurdling, hair-raising,
           nightmarish]