old style of wrench with a jaw adjustable by a screw mechanism on the handle, 1841, from monkey (n.) + wrench (n.). Monkey was used in 19c. especially by sailors, as a modifier for various types of small equipment made for specific work (monkey-block, monkey-boat, monkey-spar, etc.), and the same notion probably is behind the name of the tool. The figurative sense of "something that obstructs operations" is from the notion of one getting jammed in the gears of machinery (compare English spanner in the works).
Proto-Indo-European root forming words meaning "to turn, bend."
It forms all or part of: adverse; anniversary; avert; awry; controversy; converge; converse (adj.) "exact opposite;" convert; diverge; divert; evert; extroversion; extrovert; gaiter; introrse; introvert; invert; inward; malversation; obverse; peevish; pervert; prose; raphe; reverberate; revert; rhabdomancy; rhapsody; rhombus; ribald; sinistrorse; stalwart; subvert; tergiversate; transverse; universe; verbena; verge (v.1) "tend, incline;" vermeil; vermicelli; vermicular; vermiform; vermin; versatile; verse (n.) "poetry;" version; verst; versus; vertebra; vertex; vertigo; vervain; vortex; -ward; warp; weird; worm; worry; worth (adj.) "significant, valuable, of value;" worth (v.) "to come to be;" wrangle; wrap; wrath; wreath; wrench; wrest; wrestle; wriggle; wring; wrinkle; wrist; writhe; wrong; wroth; wry.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vartate "turns round, rolls;" Avestan varet- "to turn;" Hittite hurki- "wheel;" Greek rhatane "stirrer, ladle;" Latin vertere (frequentative versare) "to turn, turn back, be turned; convert, transform, translate; be changed," versus "turned toward or against;" Old Church Slavonic vrŭteti "to turn, roll," Russian vreteno "spindle, distaff;" Lithuanian verčiu, versti "to turn;" German werden, Old English weorðan "to become;" Old English -weard "toward," originally "turned toward," weorthan "to befall," wyrd "fate, destiny," literally "what befalls one;" Welsh gwerthyd "spindle, distaff;" Old Irish frith "against."
surname, apparently from Old English *prætt (adj.) "cunning, astute;" related to the late Old English noun prætt "a trick" (compare Middle English prat-wrench "a cunning trick;" see pretty (adj.)). As a type of pottery, named for Staffordshire pottery manufacturer Felix Pratt (1780-1859).
"to twist or wrench out of shape," early 15c. (implied in contorted), from Latin contortus, past participle of contorquere "to whirl, twist together," from assimilated form of com- "with, together," here perhaps an intensive prefix (see com-) + torquere "to twist" (from PIE root *terkw- "to twist"). Related: Contorting.
1520s, "obtain by force or compulsion; wrest away by oppressive means," from Latin extortus, past participle of extorquere "obtain by force," literally "to wrench out," from ex "out" (see ex-) + torquere "to twist" (from PIE root *terkw- "to twist"). Related: Extorted; extorting. As a past-participle adjective from early 15c.
1610s, "of the nature of or characterized by convulsion," from French convulsif, from Medieval Latin *convulsivus, from convuls-, past-participle stem of convellere "to pull away, to pull this way and that, wrench," from assimilated form of com "with, together" (see con-) + vellere "to pluck, pull violently" (see svelte). Meaning "producing or attended by convulsions" is from 1700. Related: Convulsively.