Lucarne, a word derived from the French language, stands for a type of window protruding from the roof of a building. However, a lucarne can be easily mistaken for a dormer or a skylight. If you're in search of alternative words to use for lucarne, some synonyms include roof window, dormer window, mansard window, and skylight window. Roof windows and dormer windows are similar to lucarnes in that they are both windows constructed on a sloping roof. The main difference is that roof windows are typically flush with the roofline, while dormer windows protrude. A mansard window is a subtype of dormer window designed to blend in with mansard roofs. Finally, skylight windows are typically installed on flat roofs and provide natural lighting to the interior of a building.