When plain old "fear" isn't enough to get across a deep feeling of dread about something on the horizon, use the more formal word trepidation.
"It was with a certain trepidation that I attended an advance screening of Rob Zombie's Halloween in Hollywood last night," wrote a film reviewer. Some dictionaries note that trepidation carries connotations of apprehension about an upcoming threat. In most cases, though, you can get by with the simpler word fear — why use three syllables when you could make do with one? The word comes from the Latin verb trepidare, "to tremble."