A variant spelling of 'clerestory'; a row of high windows in a church or large building that allows light to enter above the roof of a lower structure.
From 'clerestory' (from Middle English 'cler' meaning clear or bright, plus 'story' meaning a row of windows)—provides 'clear' light from above.
Medieval architects designed clerestories to create dramatic lighting effects in cathedrals—the high windows symbolized divine light entering from heaven, making the building feel sacred and otherworldly to worshippers below.
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