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]