whack2 [countable] especially spoken
the act of hitting something hard, or the noise this makes:
She gave the ball a whack.
Singleton took a whack at (=tried to hit) Miller's head.
2 British English
an amount of something
There's still a fair whack (=quite a large amount) of work to be done.
These agencies charge top whack for tickets.
3 British English
to do a fair or equal share of a job or activity:
I've done my whack of the driving - it's your turn.
4 British English take a whack at something American English
to try to do something:
'Are you any good at doing maths?' 'I'll have a whack at it.'
5 American English
all on one occasion:
Steve lost $500 in one whack.
6 American English
if a system, machine etc is out of whack, the parts are not working together correctly:
The printer's out of whack again.