While still in primary school I was collecting money for a charity, you know, shaking the tin, and a guy walked up to me and went through his pockets thoroughly. "Geez mate, I don't have a zak on me," he said. I must have looked at him with extraordinary blankness - this is a look worth perfecting my friends, believe me - because he then said, "Aw, you're probably too young to remember. A zak was a coin we had in the old days. A bit like five cents these days. Half a shilling." At the time that conversation took place Australia had changed to decimal currency and had dollars and cents rather than pounds and pence (and all the weird names). I have never heard this word used since.