'bollocks' originates from Old English, specifically the word 'bealluc' (a diminutive related to 'beall'), where 'beall' meant 'ball'.

'bealluc' in Old English developed into Middle English forms such as 'bolok'/'bollok' and later became the modern English word 'bollock' with the plural 'bollocks'.

Initially, it meant 'testicle' (a small round ball); over time it kept that anatomical meaning but also developed extended senses meaning 'nonsense' or 'rubbish' and various colloquial uses (exclamation, verb senses).