DORMER (from Lat. dormire, to sleep), in architecture, a window rising out of the roof and lighting the room in it: sometimes, however, pierced in a small gable built flush with the wall below, or corbelled out, as frequently in Scotland. In Germany, where the roofs are very lofty, there are three or four rows of dormers, one above the other, but it does not follow that the space in the roof is necessarily subdivided by floors. In some of the French châteaux the dormers (Fr. lucarne) are highly elaborated, and in some cases, as in Chambord, they form the principal architectural features. In these cases they are either placed flush with the wall or recede behind a parapet and gutter only, so as to rest on the solid wall, as they are built in stone. In Germany they assume larger proportions and constitute small gables with two or three storeys of windows. The term "dormer" arose from the windows being those of sleeping-rooms. In the phrase "dormer beam" or "dormant beam," meaning a tie-beam, we have the same sense as in the modern "sleeper."
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)