mack
n.— «Mr. Levine and his client were prisoners in California’s Lompoc Federal Correctional Complex. Like other federal inmates around the country, they found a can of mackerel—the “mack” in prison lingo—was the standard currency.» —“Mackerel Economics in Prison Leads to Appreciation for Oily Fillets” by Justin Scheck Wall Street Journal Oct. 2, 2008. (source: Double-Tongued Dictionary)
Further reading
Cat hair may be something you brush off, but cat hair is also a slang term that means “money.” In the same way, cat beer isn’t alcoholic — some people use cat beer as a joking term for “milk.” And imagine walking on a...
Have you ever googled your own name and found someone else who goes by the very same moniker? There’s a word for that: googleganger. Plus, the language of hobbyists and enthusiasts: If you’re a beekeeper, perhaps you call yourself a...