One of those great "pass the thesaurus" words which made the writings of H.P.Lovecraft so much fun to read. Characteristics within the scope of this word include elder, ancient, weird, unknown, unclean, unwholesome, possessing the capacity of driving people insane.

eldritch, adjective:
Strange or unearthly; eerie.
Possibly from elriche; the Old English "el" indicating strange, combined with "rice", meaning realm.

Also a spell-using character class from the realm of Hibernia in the Massively Multiplayer Online Roleplaying Game Dark Age of Camelot, known for using natural spells to cause massive damage.

El"dritch (?), a.

Hideous; ghastly; as, an eldritch shriek or laugh.

[Local, Eng.]

 

© Webster 1913.