In the core of the constellation concerned with the idea "terrorism" are the Greek and Latin terms "trerorn" and "tero" from which emerged "tear", giving rise to many physical and lacrimous nuances - at one edge of  the constellation are tremble or tremere which when combined with terra as in "terremoto" or trembling earth give rise to "terror" - at  another edge are ideas found in dogma, doctrines, zeal and zealotry that often fuel criminal terrorism. As ideas evolve into dogma and doctrines, attracted are those seeking solace in "faith" and among them are those prone to zeal and fanaticism. Zeal, zealot and jealousy point to "Jelousie"  or a shutter or  "a blind"  in French and illustrated by the tragic Otello who, when blinded by jealousy,  killed his beloved Desdemona. Zealots and others suffering from extremes of faith have souls and minds that are blinded or shielded from doubts without which their morality becomes feeble and easier to surrender to those offering "a cause". Terrorists, to terrorize by victimizing the innocent invoke lofty "causes" cloaked in dehumanized political and ethical arguments and others simply invoke revenge. Some say that Ernesto "Che" Guevara (a physician) demonstrated his  fidelity to Fidel Castor or the "cause" or their Cuban Revolution by offering to shoot an "infidel" "camarada". 
 
In medical parlance, tremble is to quiver and ataxia or loss of "taxis" implies dis-coordinated or altered muscular coordination, nuances explored separately.
 
When tremor extends toward terror and terrorism, the landscape becomes illuminated by artists, poets, philosophers and slogan makers as well as populated by churchmen, politicians, bandits and murderers.

"The personal has no social significance" wrote Lazar Kaganovich (a murderous henchman of Josef Stalin and architect of the "Red Terror") ...  "Dulce et decorum est pro patria mori" (it is sweet and proper to die for your country) asserted Homer ... many terrorists have listened to such words ...  "For the assassin it is an act of war, a transplant of ideals into crime" reported the journalist Jose Antonio Marina as he gazed at the carnage caused by a bomb planted by a "nationalist" in the midst of innocents.