On Fri, Apr 09, 2004 at 07:06:40AM -0700, Philippe Caquant wrote:
> By the way,  I would very much like to know the origin
> of the english word: "a nightmare". I find it very
> strange and evocative.

Yes, the "-mare" in "nightmare" comes from an OE word meaning "ghost",
ultimately from PIE *mer- which seems to have meant "to erode
(something)" or generally "to cause harm".  From the same root come
English "morbid" and Latin "mortis"; the latter is of course the
source of French "mort," English "mortal," etc.

By contrast, the word "mare" for "female horse" comes via
Proto-Germanic *marhjōn from PIE *marko-.

And then there's the Latin word "mare" = "sea", which comes from
PIE *mori-, which referred to a body of water.

For English etymologies that trace back to PIE, a good online resource is the
American Heritage Dictionary at the incredibly intuitive URL