The Collaborative International Dictionary of English v.0.48:

Frighten \Fright"en\, v. t. [imp. Frightened; p. pr. & vb. n.
   Frightening.] [See Fright, v. t.]
   To disturb with fear; to throw into a state of alarm or
   fright; to affright; to terrify.
   [1913 Webster]

         More frightened than hurt.               --Old Proverb.
   [1913 Webster]

WordNet (r) 3.0 (2006):

frighten
    v 1: cause fear in; "The stranger who hangs around the building
         frightens me"; "Ghosts could never affright her" [syn:
         frighten, fright, scare, affright]
    2: drive out by frightening

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "frighten":
   affright, agitate, alarm, alert, appall, arouse, astound, awe,
   bowl down, bowl over, browbeat, bulldoze, cow, cry havoc, cry wolf,
   curdle the blood, daunt, demoralize, discompose, disconcert,
   dismay, disquiet, distress, electrify, faze, fly storm warnings,
   fright, funk, horrify, horripilate, intimidate, jar, jolt,
   make one tremble, panic, perturb, petrify, raise apprehensions,
   scare, scare stiff, shake, shock, sound the alarm,
   sound the tocsin, spook, stagger, startle, stun, take aback,
   terrify, terrorize, unman, unnerve, unstring, upset, warn