Definition of "dormer"

Then we came to a high white wall that surrounded a large garden, and within it was a long, massive building of some beauty and pretension, with a high, latticed belfry and heavy walls and with arched dormers in the sloping roof.

1904 May, Winston Churchill, “The Strange City”, in The Crossing, New York, N.Y.: The Macmillan Company; London: Macmillan & Co., Ltd., book II (Flotsam and Jetsam), page 371

My dorm mates and I had a little get-together in our room on the second floor. We were just talking and weren't making much noise when we heard a knock on our door. It was a dormer from the room directly below us. She asked if we were cleaning and we told her that we weren't. She left but came back a little while later and asked the same question again. We asked her if our matron wants us to clean up. The dormer said no and left. But after a few minutes, she came up again and again asked if we were cleaning our room because she could hear the noise down in her room.

2004, mae, edited by Reginald Ting, True Philippine Ghost Stories #8: Spooky Dorm‎, Psicom Publishing Inc., page 38