'Terror' is Latin for 'fear that shakes the body' — from PIE *tres- (to tremble). Root of 'terrorism.'
Extreme, overwhelming fear; intense dread or fright.
From Old French 'terreur,' from Latin 'terror' (great fear, dread, alarm), from 'terrēre' (to frighten, to fill with dread, to scare), from PIE *tres- (to tremble). The Latin verb 'terrēre' is specifically causative — it means 'to cause to tremble.' The same root produced 'terrible' (causing great fear), 'terrific
'Terrific' originally meant 'causing terror' — it was a synonym for 'terrifying.' The positive flip to 'wonderful, excellent' happened gradually in the early twentieth century through ironic and hyperbolic use, making it one of the most dramatic semantic reversals in English. 'Terror' and 'terrific' share the same root
Words closest in meaning, ranked by similarity