General fear:
* Afraid
* Frightened
* Terrified
* Apprehensive
* Anxious
* Nervous
* Timid
* Worried
* Concerned
* Alarmed
Stronger fear:
* Panicked
* Horrified
* Petrified
* Paralyzed
* Intimidated
More specific emotions:
* Dread: A feeling of impending doom or fear.
* Panic: A sudden overwhelming feeling of fear.
* Terror: Extreme fear that can be paralyzing.
* Anxiety: A general feeling of unease or worry.
* Apprehension: A feeling of fear or dread about something that might happen.
More informal words:
* Scaredy-cat
* Chicken
* Jittery
* On edge
The best synonym to use will depend on the specific situation and the level of fear you want to convey.