WordWeb Online

1. Causing fear, dread or terror
   "the frightening war";
   - awful, dire, direful, dread, dreaded, dreadful, fearful, fearsome, horrendous, horrific, terrible

1. The act of inspiring with fear
   - terrorization, terrorisation [Brit]

1. Cause fear in
   "The stranger who hangs around the building frightens me";
   - fright [archaic], scare, affright
    
2. Drive out by frightening

See also: alarming, frighten off

Type of: bullying, chase away, dispel, drive away, drive off, drive out, excite, intimidation, run off, shake, shake up, stimulate, stir, turn back