c. 1600, from French trepidation (15c.) and directly from Latin trepidationem (nominative trepidatio) "agitation, alarm, trembling," noun of action from past-participle stem of trepidare "to tremble, hurry," from trepidus "alarmed, scared," from PIE *trep- (1) "to shake, tremble" (source also of Sanskrit trprah "hasty," Old Church Slavonic trepetati "to tremble"), related to *trem- (see tremble (v.)). Related: Trepidacious (1915).
1795, in specific sense of "government intimidation during the Reign of Terror in France" (March 1793-July 1794), from French terrorisme, noted in English by 1795 as a coinage of the Revolution, from Latin terror "great fear, dread, alarm, panic; object of fear, cause of alarm; terrible news," from PIE root *tres- "to tremble" (see terrible).
If the basis of a popular government in peacetime is virtue, its basis in a time of revolution is virtue and terror — virtue, without which terror would be barbaric; and terror, without which virtue would be impotent. [Robespierre, speech in French National Convention, 1794]
General sense of "systematic use of terror as a policy" is first recorded in English 1798 (in reference to the Irish Rebellion of that year). At one time, a word for a certain kind of mass-destruction terrorism was dynamitism (1883); and during World War I frightfulness (translating German Schrecklichkeit) was used in Britain for "deliberate policy of terrorizing enemy non-combatants."
The unetymological -l- is perhaps from influence of Latin latro "thief" (see larceny). Middle English had burgur (c. 1200), from Old French burgeor, burgur, also housbreker (c. 1400). Burglar-alarm is by 1840.
From c. 1500 as "fear so great as to overwhelm the mind." Meaning "quality of causing dread" is attested from 1520s. Sense of "a person fancied as a source of terror" (often with deliberate exaggeration, as of a naughty child) is recorded from 1883. Terror bombing first recorded 1941, with reference to German air attack on Rotterdam. Terror-stricken is from 1831. The Reign of Terror in French history (March 1793-July 1794) was the period when the nation was ruled by a faction whose leaders made policy of killing by execution anyone deemed an impediment to their measures; so called in English from 1801. Old English words for "terror" included broga and egesa.
"astonishment combined with terror," 1610s, from French consternation "dismay, confusion," from Latin consternationem (nominative consternatio) "confusion, dismay," noun of state from past-participle stem of consternare "overcome, confuse, dismay, perplex, terrify, alarm," which is probably related to consternere "throw down, prostrate," from assimilated form of com-, here perhaps an intensive prefix (see com-), + sternere "to spread out, lay down, stretch out" (from nasalized form of PIE root *stere- "to spread").
late 13c. distourben, "to frighten, alarm, break up the tranquility of;" c. 1300, "to stop or hinder;" from Old French destorber (Old North French distourber) and directly from Latin disturbare "throw into disorder," from dis- "completely" (see dis-) + turbare "to disorder, disturb," from turba "turmoil" (see turbid). Related: Disturbed; disturbing; disturbingly.
Middle English also had the verb as distourblen, from Old French destorbler; hence also distourbler (n.) "one who disturbs or incites" (late 14c.).
c. 1300, caucioun, "bail, guarantee, pledge," from Old French caution "security, surety" (13c.), from Latin cautionem (nominative cautio) "caution, care, foresight, precaution," noun of action from past participle stem of cavere "to be on one's guard" (from PIE root *keu- "to see, observe, perceive").
The Latin sense re-emerged in English as "prudence in regard to danger" (1650s). Meaning "word of warning, monitory advice" is from c. 1600. Meaning "anything which excites alarm or astonishment" is U.S. slang, 1835.