clerestory

1. (architecture) The upper part of a wall containing windows to let in natural light to a building, especially in the nave, transept and choir of a church or cathedral.Examples: "Following these signs, he beheld three or four men with bent bows, leaning from the clerestory gallery."; "On the Visby-Västerhejde Railway there is a steam car. [...] The upperworks consist of a short clerestory coach body with end platforms and the engine chimney protruding from the roof like a stovepipe."; "The cars built before 1913 had clerestory roofs, after the American style, and also were provided with gates and end vestibule platforms requiring gatemen."