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]

The Free On-line Dictionary of Computing (19 January 2023):

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]


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.