trepidation

Short definition from Wiktionary

Noun

1. 1
   Anxiety over the uncertain future or possible ill-occurrence.
2. 2
   An involuntary trembling, sometimes an effect of paralysis, but usually caused by terror or fear.
3. 3
   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.