ELF (O. Eng. aelf; cf. Ger. Alp, nightmare), a diminutive supernatural being of Teutonic mythology, usually of a more or less mischievous and malignant character, causing diseases and evil dreams, stealing children and substituting changelings, and thus somewhat different from the Romanic fairy, which usually has less sinister associations. The prehistoric arrow-heads and other flint implements were in England early known as "elf-bolts" or "elf-arrows," and were looked on as the weapons of the elves, with which they injured cattle. So too a tangle in the hair was called an "elf-lock," as being caused by the mischief of the elves.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)