Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

   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.

   Syn: Tremor; agitation; disturbance; fear.

Source : WordNet®

trepidation
     n : a feeling of alarm or dread