Source : Webster's Revised Unabridged Dictionary (1913)

Terrify \Ter"ri*fy\, v. t. [imp. & p. p. {Terrified}; p. pr. &
   vb. n. {Terrifying}.] [L. terrere to frighten + -fy: cf. F.
   terrifier, L. terrificare. See {Terrific}, and {-fy}.]
   1. To make terrible. [Obs.]

            If the law, instead of aggravating and terrifying
            sin, shall give out license, it foils itself.
                                                  --Milton.

   2. To alarm or shock with fear; to frighten.

            When ye shall hear of wars . . . be not terrified.
                                                  --Luke xxi. 9.

Source : WordNet®

terrifying
     adj : causing extreme terror; "a terrifying wail" [syn: {terrific}]