nightmarish

from WordNet (r) 3.0 (2006)

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

from The Collaborative International Dictionary of English v.0.48

nightmarish \nightmarish\ adj.
   Terrifying, as if in a nightmare[2]; resembling a
   nightmare[2].

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