The Collaborative International Dictionary of English v.0.48:

Horrify \Hor"ri*fy\, v. t. [imp. & p. p. Horrified; p. pr. &
   vb. n. Horrifying.] [L. horrificare. See Horrific.]
   To cause to feel horror; to strike or impress with horror;
   as, the sight horrified the beholders. --E. Irving.
   [1913 Webster]

WordNet (r) 3.0 (2006):

horrified
    adj 1: stricken with horror [syn: horrified, horror-
           stricken, horror-struck]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "horrified":
   aghast, appalled, ashen, astounded, awed, awestricken, awestruck,
   blanched, cowed, deadly pale, frozen, gray with fear,
   horror-struck, intimidated, pale as death, pallid, paralyzed,
   petrified, scared stiff, scared to death, stunned, stupefied,
   terrified, terror-crazed, terror-haunted, terror-ridden,
   terror-riven, terror-shaken, terror-smitten, terror-struck,
   terror-troubled, undone, unmanned, unnerved, unstrung