The Collaborative International Dictionary of English v.0.48:

Startle \Star"tle\ (st[aum]r"t'l), v. i. [imp. & p. p.
   Startled (st[aum]r"t'ld); p. pr. & vb. n. Startling
   (st[aum]r"tl[i^]ng).] [Freq. of start.]
   To move suddenly, or be excited, on feeling alarm; to start.
   [1913 Webster]

         Why shrinks the soul
         Back on herself, and startles at destruction?
                                                  --Addison.
   [1913 Webster]

WordNet (r) 3.0 (2006):

startling
    adj 1: so remarkably different or sudden as to cause momentary
           shock or alarm; "Sydney's startling new Opera House";
           "startling news"; "startling earthquake shocks"

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "startling":
   abrupt, alarming, amazing, astonishing, astounding, awesome, awing,
   breathtaking, chilling, confounding, daunting, deterrent,
   deterring, disconcerting, discouraging, disheartening, dismaying,
   disquieting, disturbing, electrifying, eye-opening, fear-inspiring,
   fearful, fearsome, frightening, frightful, hasty, headlong,
   impetuous, impulsive, jarring, jolting, mind-boggling,
   nerve-shattering, overawing, overwhelming, precipitant,
   precipitate, precipitous, quick, scaring, scary, shocking,
   spectacular, speedy, staggering, stunning, sudden, surprising,
   swift, terrifying, unanticipated, unexpected, unforeseen,
   unlooked-for, unpredicted, unsettling, upsetting