cash on the barrelhead

Money paid immediately for a purchase, as in “I’ll give you $50 for that bike, cash on the barrelhead.” Why hard cash should be equivalent to putting money on the flat head of a barrel is unclear. In nineteenth-century America barrel was slang for money, especially for a slush fund provided for a political candidate, and a barrel of money signified a huge fortune. However, these usages are only loosely related to the cliché, which itself may be dying out.