Whack

verb (used with object)
1.
to strike with a smart, resounding blow or blows.
2.
Slang. to divide into or take in shares (often followed by up):
Whack the loot between us two.
verb (used without object)
3.
to strike a smart, resounding blow or blows.
noun
4.
a smart, resounding blow:
a whack with his hand.
5.
Informal. a trial or attempt:
to take a whack at a job.
6.
Slang. a portion or share.
Verb phrases
7.
whack off,

to cut off or separate with a blow:
The cook whacked off the fish’s head.
Slang: Vulgar. to masturbate.

8.
whack out, Slang. to produce quickly or, sometimes, carelessly:
She whacks out a short story every week or so.
Idioms
9.
out of whack, Informal. out of order or alignment; not in proper condition.
verb (transitive)
1.
to strike with a sharp resounding blow
2.
(usually passive) (Brit, informal) to exhaust completely
3.
(transitive; usu foll by in or on) (informal) to put something on to or into something else with force or abandon: whack on some sunscreen
noun
4.
(transitive) (US, slang) to murder: if you were out of line you got whacked
5.
a sharp resounding blow or the noise made by such a blow
6.
(informal) a share or portion
7.
(informal) a try or attempt (esp in the phrase have a whack at)
8.
(informal) out of whack, out of order; unbalanced: the whole system is out of whack
interjection
9.
an exclamation imitating the noise of a sharp resounding blow
vogue
wetware

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]