'ballsy' originates from English, specifically the noun 'balls', where 'balls' meant 'testicles' and by extension 'courage' (slang).

'ballsy' changed from the slang noun 'balls' combined with the adjectival suffix '-y' in mid-20th century American English, producing 'ballsy' and later comparative forms such as 'ballsier'.

Initially it referred literally to 'having balls' (testicles); over time it evolved into the figurative meaning 'courageous, audacious', and now functions as an informal/slang adjective meaning 'bold' (sometimes coarse).