Nightmares Question: Why do we call a bad dream a nightmare? Answer: Most people when asked to guess about its origins figure that the "mare" in nightmare has something to do with horses. I could live with that. Recently I was given a hot tip on a thoroughbred and got to the betting window at the track just as the race began and the window closed. The nag won and I did not have good dreams that night. But that's not the etymology of nightmare--not by a long shot. It comes from the Old English word "maere," which means an incubus, a tiny demon that stands on your chest during the night, suffocating you. Why would an incubus do that to you? You probably did something to upset nature's laws. Maybe you served white wine with red meat, wore a red suit with brown shoes, or did some other nightmarish thing.   (Source: THE OXFORD DICTIONARY OF ENGLISH ETYMOLOGY)