'ballsy' originates from American English, specifically from the noun 'balls' (slang for testicles) with the adjectival suffix '-y' added to mean 'characterized by'.

'ballsy' developed in the mid-20th century from the slang noun 'balls' (used figuratively for courage). The formation follows a common pattern of adding '-y' to a noun to create an adjective meaning 'having or characterized by [noun]'.

Initially the source word referred literally to 'testicles'; over time the derived adjective came to mean 'having courage or audacity' (a figurative extension).