A testicle (British slang, considered vulgar); also used as an exclamation or insult.
Of uncertain origin, possibly related to 'bollock' (testicle), which itself comes from Old English 'beallucas.' British slang that has been documented since at least the 17th century.
British insults often involve body parts—'collock,' 'bollock,' and 'git' all reflect how English slang varies wildly by region, and what's funny in London might confuse someone from New York.
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