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]

The Collaborative International Dictionary of English v.0.48:

Startle \Star"tle\ (st[aum]r"t'l), v. t.
   1. To excite by sudden alarm, surprise, or apprehension; to
      frighten suddenly and not seriously; to alarm; to
      surprise.
      [1913 Webster]

            The supposition, at least, that angels do sometimes
            assume bodies need not startle us.    --Locke.
      [1913 Webster]

   2. To deter; to cause to deviate. [R.] --Clarendon.
      [1913 Webster]

   Syn: To start; shock; fright; frighten; alarm.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Startle \Star"tle\, n.
   A sudden motion or shock caused by an unexpected alarm,
   surprise, or apprehension of danger.
   [1913 Webster]

         After having recovered from my first startle, I was
         very well pleased with the accident.     --Spectator.
   [1913 Webster]

WordNet (r) 3.0 (2006):

startle
    n 1: a sudden involuntary movement; "he awoke with a start"
         [syn: startle, jump, start]
    v 1: to stimulate to action ; "..startled him awake";
         "galvanized into action" [syn: startle, galvanize,
         galvanise]
    2: move or jump suddenly, as if in surprise or alarm; "She
       startled when I walked into the room" [syn: startle,
       jump, start]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "startle":
   affright, alarm, alert, amaze, arouse, astonish, astound, awe,
   awestrike, be startled, bedaze, bedazzle, bewilder, boggle, bolt,
   bowl down, bowl over, confound, cry havoc, cry wolf,
   curdle the blood, daze, dazzle, discombobulate, discompose, dismay,
   disquiet, disturb, dumbfound, dumbfounder, electrify, fight shy,
   flabbergast, flinch, fly storm warnings, fright, frighten, funk,
   horripilate, jar, jib, jolt, jump, jump a mile, make one tremble,
   overwhelm, panic, paralyze, perplex, perturb, petrify,
   raise apprehensions, scare, shake, shake up, shock, shy, skedaddle,
   sound the alarm, sound the tocsin, spook, spring, stagger,
   stampede, start, start aside, strike dead, strike dumb,
   strike with wonder, stun, stupefy, surprise, take aback, terrify,
   terrorize, unman, unnerve, unsettle, unstring, upset, warn