Bold, daring, or courageous; showing great confidence and willingness to take risks.
From 'balls,' slang for courage or nerve that arose in the early 20th century from the testicles as a symbol of masculine bravery; combined with adjective suffix '-y.'
The slang term 'balls' for courage originally came from anatomy—medieval warriors and gladiators needed to be physically tough in vulnerable places, making the metaphor stick for thousands of years.
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