The Collaborative International Dictionary of English v.0.48:

Tweak \Tweak\, v. t. [OE. twikken, originally the same word as
   twicchen; cf. LG. twikken. See Twitch.]
   To pinch and pull with a sudden jerk and twist; to twitch;
   as, to tweak the nose. --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tweak \Tweak\, n.
   1. A sharp pinch or jerk; a twist or twitch; as, a tweak of
      the nose. --Swift.
      [1913 Webster]

   2. Trouble; distress; tweag. [Obs.]
      [1913 Webster]

   3. A prostitute. [Obs.] --Brathwait.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tweak
    n 1: a squeeze with the fingers [syn: pinch, tweak]
    v 1: pinch or squeeze sharply
    2: pull or pull out sharply; "pluck the flowers off the bush"
       [syn: pluck, tweak, pull off, pick off]
    3: adjust finely; "fine-tune the engine" [syn: fine-tune,
       tweak]

Moby Thesaurus II by Grady Ward, 1.0:

111 Moby Thesaurus words for "tweak":
   acute pain, afflict, agonize, ail, bite, bob, boring pain, burn,
   chafe, charley horse, clamp, clamping, clamping down, compress,
   compression, convulse, cramp, cramps, crick, crucify, crush, cut,
   darting pain, distress, ensphere, excruciate, fester, flick, flip,
   flirt, flounce, fret, fulgurant pain, gall, girdle pain, give pain,
   gnaw, gnawing, grate, grind, grip, gripe, griping, harrow, hitch,
   hurt, inflame, inflict pain, irritate, jerk, jig, jigger, jigget,
   jiggle, jog, joggle, jumping pain, kill by inches, kink, lacerate,
   lancinating pain, martyr, martyrize, nip, pain, pang, paroxysm,
   pierce, pinch, pluck, press, pressure, prick, prolong the agony,
   put to torture, rack, rankle, rasp, rub, seizure, sharp pain,
   shoot, shooting, shooting pain, snake, snatch, spasm, squeeze,
   squeezing, stab, stabbing pain, start, sting, stitch, sudden pull,
   thrill, throes, tighten, tightening, tormen, torment, torture,
   twinge, twist, twitch, wad up, wound, wrench, wring, yank, yerk



The Jargon File (version 4.4.7, 29 Dec 2003):

tweak
 vt.

    1. To change slightly, usually in reference to a value. Also used
    synonymously with twiddle. If a program is almost correct, rather than
    figure out the precise problem you might just keep tweaking it until it
    works. See frobnicate and fudge factor; also see shotgun debugging.

    2. To tune a program; preferred usage in the U.K.


The Free On-line Dictionary of Computing (30 December 2018):

tweak

   1. To change slightly, usually in reference to a value.  Also
   used synonymously with twiddle.  If a program is almost
   correct, rather than figure out the precise problem you might
   just keep tweaking it until it works.  See frobnicate and
   fudge factor; also see shotgun debugging.

   2. To tune or bum a program; preferred usage in the UK.

   [Jargon File]