The act or process of running down or descending; a downward course or movement.
From Latin 'decursio', derived from 'decurrere' (to run down), with the '-ion' suffix indicating an action or process.
A decursion is literally 'the act of running down,' and while it's archaic now, it perfectly described how Romans understood things moving downward—from the decursion of a valley to the decursion of a sword strike.
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