WordWeb Online

1. Very great or intense
   "a terrific noise"; "a terrific thunderstorm"; "fought a terrific battle"
    
2. Extraordinarily good or great; used especially as an intensifier
   "a terrific trip to the Orient";
   - fantastic, grand, howling [informal], marvelous [US], marvellous [Brit, Cdn], rattling [informal], tremendous, wonderful, wondrous, phenomenal, epic [slang], magnificent, heavenly [informal]
    
3. [archaic] Causing extreme terror
   "a terrific wail";
   - terrifying

See also: alarming, extraordinary, intense

Encyclopedia: Terrific