Origins
The word 'torture' preserves, at its etymological core, an image of physical twisting — the wrenching of limbs, the turning of the rack, the distortion of the human body into positions it was never meant to occupy. Every modern meaning, including the figurative ('this suspense is torture'), traces back to this single, visceral metaphor.
The word enters English in the mid-sixteenth century from French 'torture,' which descends from Late Latin 'tortūra' (a twisting, a wringing, a tormenting). Late Latin 'tortūra' is a noun formed from 'tortus,' the past participle of Classical Latin 'torquēre' (to twist, to wrench, to turn, to distort). The verb 'torquēre' traces to PIE *terkʷ- (to twist, to wind).
The Latin verb 'torquēre' is exceptionally productive in English through its various prefixed forms and derivatives. 'Contort' (from 'contorquēre,' to twist together) describes something twisted out of its natural shape. 'Distort' (from 'distorquēre,' to twist apart) means to warp or misrepresent. 'Extort' (from 'extorquēre,' to twist out, to wrench away) originally described the physical wresting of something from someone's grasp, then metaphorically the coercion of money or confessions. 'Retort' (from 'retorquēre,' to twist back) originally meant to turn an argument back against its maker.
Proto-Indo-European Roots
'Torque,' the physics term for a rotational force, comes directly from Latin 'torquēre' — it is the most literal survivor of the root, preserving the pure meaning of twisting. 'Torch' has a less obvious connection: it derives from Old French 'torche,' from Vulgar Latin *torca, from Latin 'torqua' or 'torques' (a twisted thing), because early torches were bundles of twisted fibers soaked in wax or pitch. 'Torment' takes a slightly different path, from Latin 'tormentum' (an instrument for twisting or hurling, a rack, an engine of war), itself from 'torquēre.'
The legal use of torture — the infliction of pain to extract confessions — was a standard feature of Roman law, though initially restricted to slaves. Medieval European legal systems inherited and expanded the practice. The word 'tortūra' in Late Latin referred specifically to this judicial procedure before broadening to mean any infliction of extreme suffering. In English, the legal and general senses coexisted from the word's first appearance.
An unexpected relative is 'tortilla,' the Mexican flatbread. Spanish 'tortilla' is a diminutive of 'torta' (a round cake or bread), from Late Latin 'torta' (a twisted bread or cake), from the feminine past participle of 'torquēre.' The connection is the twisting or turning involved in shaping the dough. Thus the vocabulary of baking and the vocabulary of cruelty meet in the same Latin verb for twisting — a reminder that etymology is indifferent to the moral weight of the words it connects.