eldritch

From the earlier form elritch, of uncertain origin. The second element, -ritch, is generally taken to be Old English rīċe (“realm, kingdom”). Some think that the first element, el-, derives from an Old English root meaning “foreign, strange, other” (related to Old English ellende and modern English else); others think that it derives from elf. It was reintroduced into popular literature by the writings of H. P. Lovecraft.

来源：wiktionary