To stir or agitate something vigorously, or to produce butter by shaking cream in a container repeatedly.
From Old English 'cyrne' and Proto-Germanic roots meaning to turn or rotate. Originally a literal tool and action for making butter, it metaphorically expanded to mean any vigorous, repetitive motion.
Before refrigeration, every household had a butter churn, and the repetitive action was so common that 'churn' became the perfect word for the stomach-turning feeling of anxiety—your guts literally feel like they're being churned!
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