Etymology
Advertisement
wrench (v.)
Old English wrencan "to twist," from Proto-Germanic *wrankjan (source also of Old High German renken, German renken "to twist, wrench," Old English wringan "to wring"), from PIE *wreng- "to turn" (source also of Sanskrit vrnakti "turns, twists," Lithuanian rengtis "to grow crooked, to writhe"), nasalized variant of *werg- "to turn" (source also of Latin vergere "to turn, tend toward"), from root *wer- (2) "to turn, bend." Related: Wrenched, wrenching.
Related entries & more 
Advertisement
wrench (n.)
Old English wrenc "a twisting, artifice, trick;" see wrench (v.). The meaning "tool with jaws at one end for turning or holding" is first recorded 1794.
Related entries & more 
monkey-wrench (n.)

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). 

Related entries & more 
*wer- (2)

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."

Related entries & more 
Allen 
masc. proper name and surname, variant of Alan (q.v.). In reference to a wrench, key, screw, etc. with a hexagonal socket or head, 1913, from the Allen Manufacturing Company of Hartford, Connecticut, U.S.
Related entries & more 
Advertisement
Pratt 

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).

Related entries & more 
contort (v.)

"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.

Related entries & more 
extort (v.)

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.

Related entries & more 
convulsive (adj.)

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.

Related entries & more 
spanner (n.)
1630s, a tool for winding the spring of a wheel-lock firearm, from German Spanner, from spannen "to join, fasten, extend, connect," from Proto-Germanic *spannan, from PIE root *(s)pen- "to draw, stretch, spin" (source also of spin (v.)). Meaning "wrench" is from 1790. Figurative phrase spanner in the works attested from 1921 (Wodehouse).
Related entries & more