To remove the official money status from a currency or to remove something's monetary value.
From de- (remove) + monetize (make into money). Monetize comes from Latin moneta meaning coin. The verb form allows the action to be described.
When governments demonetize old bills, it's often a tool to fight corruption and tax evasion, but it can also create chaos—people holding stacks of suddenly-worthless cash have only a limited time to exchange them.
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