Im partly spanish descendant so i might not get the whole idea of [b]Night/bMare (female horse or/and moon dark regions.
In spanish they are called “pesadilla” which is the literally translated as “little heavy one” or something along that. So in spanish we understand it as “heavy dreams” whereas in english it’s a nocturnal-femal-horse if the word’s taken literally OR nocturnal moon dark region.
So why are the "nightmares(bad dreams) called “nightmares”?
i want to find out clearly the why of that.
The idea i get so far is that because the “Mares”(seas) are the dark areas of the surface of the moon they resemble the dark content of bad dreams. is that right?
The original meaning of nightmare wasn’t a bad dream, but something like a sleep paralysis or old hag experience if I recall correctly. I guess it later slowly lost the original meaning and became a word for bad dream…
On the meaning of ‘nightmare’, Wikipedia says the following:
“Such nightmares were widely considered to be the work of demons, which were thought to sit on the chests of sleepers. In Old English, the being in question was called a mare or mære (from a proto-Germanic *marōn, related to Old High German and Old Norse mara), whence comes the mare part in nightmare.”
So…nothing to do with a noctunal dark moon region. Or horses. Probably.
That’s pretty cool, I was trying to look it up before but couldn’t find anything. Wiki I actually checked first, but I didn’t get far before being distracted. (probably by a shiny object or flashy ad ) Thanks for the info though, CD’s question interested me.
Yeah Wolb; I was wondering about the “mare”, but it is not female horse nor moon dark regions. It’s a demon in the mythology apparently so that leaves us to “having a night with demons” or something along that i think.
As I understand it, a nightmare is a night-demon, or at least that was the meaning of the word until it changed into “bad dream” - we still use the same word to describe the same thing, but because we live in the age of reason, it’s not a nasty demon, but a bad dream.
Compliments and adoration to Aikanaro for finding the definition, and with the source quoted, too! Fellow academic at heart? (And isn’t wikipedia wonderful?)
“The mare in nightmare is not a female horse, but a mara, an Anglo-Saxon and Old Norse term for a demon that sat on sleepers’ chests, causing them to have bad dreams.”
Mara is a female deamon that likes to sit on people, causing them to have a suffocating experience. Mara actually means something along the lines of “feeling of asphyxiation”.
Human females could actually, during nightly hours, be converted into Maras and “ride” sleeping people. And no, it wouldn’t be a pleasurable experience, even for a male.
The Mara also enjoyed riding horses and braiding their manes. But nothing was more alluring than to ride the branches of a pine tree. So to protect the horses, the stable masters often nailed a pine twig outside the stables, so that the Mara would leave the horses alone.
Anyway, in Swedish, we call nightmares “mardrömmar” which can be transelated as: “Dreams about Mara”. So, at least in Swedish, that’s where the name originates from.
My source of information was the Swedish wiki-pages.
We have this exact word in polish- mara and nocna mara(or zmora) which stands for scary night ghost.Also means something close to hallucination, not sharp,foggy.I.e some of swamp smokes or other man/woman shaped shadows can be called this.
Not much used in todays vocabulary.
) Thanks for the info though, CD’s question interested me. 
to Aikanaro for finding the definition, and with the source quoted, too! Fellow academic at heart? (And isn’t wikipedia wonderful?)
