Never done or known before. It describes events or situations that have no earlier example to follow.
From 'un-' (not) + 'precedented' (having a precedent), from Latin 'praecēdere' (to go before). It became common in English in the 1600s.
Precedent is a 'before example', so unprecedented literally means 'with no example before it'. That’s why you often see it in news headlines when something breaks all the usual patterns.
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