Almost like a picture in a pop-up book, a dormer is a peaked extension, with a window, that rises up from the roof of a house. The word dormer often refers to the window itself.
A dormer, with roots in the French dormir (“to sleep”), often extends from an upstairs bedroom. The word has a sense of old-fashioned charm about it. Though you may occasionally still see a face peeking out from a dormer, the word brings to mind old stories such as the Hans Christian Andersen fairytale, “The Snow Queen”: “They each had a little dormer window, and one only had to step over the gutter to get from one house to the other.”