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]

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

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]


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.