To put in peril; to endanger or expose to risk or danger.
From em- (cause to be in) + peril. A now-archaic verb that competed with the more common word 'imperil,' which eventually won out.
This is a fascinating near-miss in English word history—both 'emperil' and 'imperil' existed and meant the same thing, but 'imperil' (with the im- prefix) became standard. Language has these quiet competitions where one word wins out.
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