clear-story

Or clerestory, an upper story, or row of windows in a Gothic church rising well above the adjoining parts of the building (in contradistinction to the blindstory, often called the triforium). In churches it appears to have been adopted as a means of obtaining an increase of light in the body of the building; but the windows are not unfrequently so small that they serve this purpose very imperfectly… (Parker, 1896)