Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

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

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

Source : WordNet®

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

Source : Free On-Line Dictionary of Computing

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}]