The Collaborative International Dictionary of English v.0.48:

Trepidation \Trep`i*da"tion\, n. [F. tr['e]pidation, L.
   trepidatio, fr. trepidare to hurry with alarm, to tremble,
   from trepidus agitated, disturbed, alarmed; cf. trepit he
   turns, Gr. ? to turn, E. torture.]
   1. An involuntary trembling, sometimes an effect of
      paralysis, but usually caused by terror or fear; quaking;
      quivering.
      [1913 Webster]

   2. Hence, a state of terror or alarm; fear; confusion;
      fright; as, the men were in great trepidation.
      [1913 Webster]

   3. (Anc. Astron.) A libration of the starry sphere in the
      Ptolemaic system; a motion ascribed to the firmament, to
      account for certain small changes in the position of the
      ecliptic and of the stars.
      [1913 Webster]

   Syn: Tremor; agitation; disturbance; fear.
        [1913 Webster]

WordNet (r) 3.0 (2006):

trepidation
    n 1: a feeling of alarm or dread

Moby Thesaurus II by Grady Ward, 1.0:

124 Moby Thesaurus words for "trepidation":
   agitation, alarm, apprehensiveness, attack of nerves, bluster,
   bobbery, boil, boiling, brouhaha, buck fever, bustle,
   case of nerves, chills of fear, churn, cold creeps, cold shivers,
   cold sweat, commotion, consternation, conturbation, creeps, didder,
   discomposure, dismay, disorder, disquiet, disquietude, disturbance,
   dithers, dread, ebullition, embroilment, excessive irritability,
   excitement, fear, fear and trembling, ferment, fermentation, fever,
   feverishness, fidgetiness, fidgets, flap, flurry, fluster, flutter,
   flutteration, foment, fright, fume, fuss, goose bumps, gooseflesh,
   heartquake, heaving, horripilation, horror, hubbub, hurly-burly,
   inquietude, jimjams, jitters, jumpiness, maelstrom, malaise, moil,
   morbid excitability, nerves, nerviness, nervosity, nervous stomach,
   nervousness, palpitation, panic, panickiness, panting,
   perturbation, pitapat, pitter-patter, quaking, quaver, quavering,
   quiver, quiver of terror, quivering, restlessness, roil, rout, row,
   seethe, seething, shakes, shaking, shiver, shivers, shudder,
   spell of nerves, stage fright, state of nerves, stir, sweat, swirl,
   terror, thrill of fear, throb, throbbing, tic, to-do, tremble,
   trembling, tremor, trepidity, tumult, tumultuation, turbidity,
   turbulence, turmoil, twitching, twitter, unease, uneasiness,
   unrest, upset, vellication