A falling down; a descent, drop, or decline; also, a heavy downpour of rain.
From 'down' (downward direction) plus 'come' (to arrive); describes something moving or falling downward, with the earliest uses appearing in Middle English texts.
A 'downcome' of rain is a wonderfully poetic way to describe a storm—it's what the rain does, it comes down upon you! Medieval English loved these compound words that describe natural phenomena with vivid action verbs.
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