A horizontal piece of wood, stone, or metal at the bottom of a window or door frame; another spelling of 'sill.'
From Old English 'syll' and Old Germanic roots meaning 'threshold' or 'base.' The word has remained relatively unchanged for over a thousand years, describing the same architectural feature.
The humble cill has been keeping water out of buildings since before English was even really English—it's one of those words and things that's so basic we forget someone had to invent the concept!
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