A vulgar slang word for testicle, or as a verb, to scold or criticize someone harshly (primarily British English).
From Old English 'ballock' or 'bealluc,' related to 'ball.' The term has been used as anatomical slang for centuries, and the verb meaning 'to scold' developed from the idea of harsh confrontation.
British English has dozens of slang terms for this body part—'bollock,' 'bollocks,' 'knackers,' 'nads'—and the word 'bollocks' used alone means 'nonsense,' probably because people found the word's sound funny enough to apply to absurdity, making it one of the most versatile rude words in English.
Complete word intelligence in one call. Free tier — 50 lookups/day.