Directed downward; sad, dejected, or feeling hopeless; also, a mining shaft through which air is forced downward.
From 'down' (downward) plus 'cast' (to throw or direct); originally described eyes looking downward, metaphorically indicating sadness or shame.
When you're sad, you literally look down—and English captured this universal human experience in this single perfect word! In mining, a 'downcast' shaft is how miners survived: fresh air was forced down so they wouldn't suffocate in those dark tunnels.
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