Definition of "zack"

zack

/zak/

noun
plural zacks
1. (Australia) Sixpence.
  Quotations
  "Strewth, Dad! It's not worth a zack!" said Barry.
  2014, Frank E. Burdett, The Purple Tree: The Queensland Outback in the 1860s
2. (Australia, rare) Five cents.
3. (Australia) A six-month or six-year prison sentence.