The Collaborative International Dictionary of English v.0.48:

Terrorist \Ter"ror*ist\, n. [F. terroriste.]
   1. One who governs by terrorism or intimidation;
      specifically, an agent or partisan of the revolutionary
      tribunal during the Reign of Terror in France. --Burke.
      [1913 Webster]

   2. One who commits terrorism[2].
      [PJC]

WordNet (r) 3.0 (2006):

terrorist
    n 1: a radical who employs terror as a political weapon; usually
         organizes with other terrorists in small cells; often uses
         religion as a cover for terrorist activities

Moby Thesaurus II by Grady Ward, 1.0:

121 Moby Thesaurus words for "terrorist":
   Bolshevik, Bolshevist, Bolshie, Carbonarist, Carbonaro, Castroist,
   Castroite, Charley, Communist, Cong, Fenian, Guevarist, Jacobin,
   Leninist, Mafioso, Maoist, Marxist, Mau-Mau, Puritan, Red,
   Red Republican, Roundhead, Sinn Feiner, Trotskyist, Trotskyite, VC,
   Vietcong, Yankee, Yankee Doodle, Young Turk, alarmist, anarch,
   anarchist, annihilator, arsonist, assassin, beast, beldam, berserk,
   berserker, biblioclast, bomber, bonnet rouge, brute, burner,
   criminal, criminal syndicalist, demolisher, demon, desperado,
   destroyer, devil, dragon, dynamitard, dynamiter, exterminator,
   felon, fiend, fire-eater, firebrand, fury, goon, gorilla, gunman,
   gunsel, hardnose, hell-raiser, hellcat, hellhound, hellion,
   holy terror, hood, hoodlum, hothead, hotspur, hun, iconoclast,
   idol breaker, idoloclast, incendiary, insurgent, killer, mad dog,
   madcap, monster, mugger, nihilist, radical, rapist, rebel, red,
   revolutionary, revolutionary junta, revolutioner, revolutionist,
   revolutionizer, ruiner, sans-culotte, sans-culottist, savage,
   scaremonger, she-wolf, spitfire, subversive, syndicalist,
   termagant, terror, thug, tiger, tigress, tough, tough guy,
   ugly customer, vandal, violent, virago, vixen, wild beast, witch,
   wolf, wrecker