1. Elliptical, rectangular, segmental-headed, or semicircular-headed window, to illuminate a volume within a pitched roof. Its front is usually built of the same material as the wall of the building's main façade, is constructed on that wall, lines up with the naked of the wall, so often a strong architectural feature (known as a Flemish gable), and is positioned over the entablature. It is distinct from a dormer, which rises from the slope of a roof and is normally of light construction.
2. Small gabled aperture on the sloping sides of a Gothic spire, constructed of the same material.
"lucarne." A Dictionary of Architecture and Landscape Architecture. . Encyclopedia.com. (August 17, 2018). http://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/lucarne
"lucarne." A Dictionary of Architecture and Landscape Architecture. . Retrieved August 17, 2018 from Encyclopedia.com: http://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/lucarne