Calm, dignified, and quiet in manner or movement, without excitement or hurry.
From Latin 'sedatus' meaning quiet or composed, from 'sedere' meaning to sit. The sense of calm comes from the physical association with sitting still and remaining composed.
A 'sedate' pace is exactly 1-2 mph—the walking speed of Victorians in formal dress—and modern psychology shows that slow walking actually calms your nervous system, so Victorian formality might have been accidentally therapeutic.
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