Converting something (usually a check) into money, or taking advantage of an opportunity.
From Old French 'casse' meaning money box or till, derived from Latin 'capsa' (box, container). 'Cashing in' evolved to mean exchanging something of value for actual cash.
The phrase 'cashing in' on something originally meant turning a check into real money, but now athletes 'cash in' on endorsements and people 'cash in' on opportunities—the metaphor of converting potential into actual gain.
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