The Collaborative International Dictionary of English v.0.48:

Whack \Whack\, v. t. [imp. & p. p. Whacked; p. pr. & vb. n.
   Whacking.] [Cf. Thwack.]
   1. To strike; to beat; to give a heavy or resounding blow to;
      to thrash; to make with whacks. [Colloq.]
      [1913 Webster]

            Rodsmen were whackingtheir way through willow
            brakes.                               --G. W. Cable.
      [1913 Webster]

   2. To divide into shares; as, to whack the spoils of a
      robbery; -- often with up. [Slang]
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Whack \Whack\, v. i.
   To strike anything with a smart blow.
   [1913 Webster]

   To whack away, to continue striking heavy blows; as, to
      whack away at a log. [Colloq.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Whack \Whack\, n.
   1. A smart resounding blow. [Colloq.]
      [1913 Webster]

   2. A portion; share; allowance. [Slang]
      [Webster 1913 Suppl.]

   3. an attempt; as, to take a whack at it. [Colloq.]
      [PJC]

   Out of whack, out of order. [Slang]
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

whack
    n 1: the sound made by a sharp swift blow
    2: the act of hitting vigorously; "he gave the table a whack"
       [syn: knock, belt, rap, whack, whang]
    v 1: hit hard; "The teacher whacked the boy" [syn: whack,
         wham, whop, wallop]

Moby Thesaurus II by Grady Ward, 1.0:

129 Moby Thesaurus words for "whack":
   approach, assay, attempt, bang, bash, bat, beating, belt, bid,
   biff, blow, bonk, bout, box, box the ears, buffet, bump, burst,
   bust, catch, chance, chop, clap, clash, clip, clobber, clout,
   clump, coldcock, crack, crash, crump, cuff, cut, dash, deal,
   deal a blow, deck, dig, ding, dint, drub, drubbing, drumming,
   effort, endeavor, essay, experiment, fetch, fetch a blow, flap,
   fling, flop, fusillade, gambit, go, hit, hit a clip, inning,
   innings, jab, knock, knock cold, knock down, knock out,
   let have it, lick, move, offer, opportunity, paste, pelt, place,
   plunk, poke, pop, pound, punch, rap, relief, report, round, say,
   shot, slam, slap, slap the face, slat, slog, slug, smack, smash,
   smite, snap, soak, sock, spell, splat, stab, stagger, step, strike,
   strike at, stroke, strong bid, swap, swat, swing, swipe, tap,
   tattoo, tentative, thump, thwack, time, time at bat,
   token punishment, trial, trial and error, try, turn, undertaking,
   wallop, wham, whap, whirl, whomp, whop, yerk



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

whack
 v.

    According to arch-hacker James Gosling (designer of NeWS, GOSMACS and
    Java), to ?...modify a program with no idea whatsoever how it works.? (See
    whacker.) It is actually possible to do this in nontrivial circumstances
    if the change is small and well-defined and you are very good at glarking
    things from context. As a trivial example, it is relatively easy to change
    all stderr writes to stdout writes in a piece of C filter code which
    remains otherwise mysterious.


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

whack

   According to arch-hacker James Gosling, to "...modify a
   program with no idea whatsoever how it works." (See
   whacker.)  It is actually possible to do this in nontrivial
   circumstances if the change is small and well-defined and you
   are very good at glarking things from context.  As a trivial
   example, it is relatively easy to change all "stderr" writes
   to "stdout" writes in a piece of C filter code which remains
   otherwise mysterious.

   [Jargon File]