Nightmares are a mythical beast. They are a pitch black horse which rides through the sky and has trail of flame burning from each of its hooves into a brilliant tail that streaks behind the beast as it rides through the sky. These horses were said to be seen only at night, swooping down from the sky to viciously attack any unwary beings travelling through the night. Said victims, according to mythology, were lobbied with varying magical attacks, and once the victims were dead the nightmare would ride off into the night, not returning to attack until the next night.

The way its name was derived is still unsure, however there are three main theories. The first is that the name simply implies a night-mare, a mare being a name for a female horse, and the fact that this horse was only seen at night the name night-mare became common usage, without the hyphen of course. The second, and probably the most popular, is that the flame horse was "the stuff of nightmares" and so people began calling it a nightmare, as one could only conjure up such a horrid beast in a nightmare. The third, and least popular theory, is that the horse's pure black coat earned it the name nightmare, as nightmares are dark and terrifying, as was the horse.

I shall leave it up to you to decide on the correct theory.