Emily Dickinson Lexicon

ELF, n. [plur. Elves. Sax. ælf, or elfenne, a spirit, the nightmar; a ghost, hag or witch; Sw. älfver. In W. el is a moving principle, a spirit; elv is the same; elu is to move onward, to go; elven is an operative cause, a constituent part, an element; and elf is what moves in a simple or pure state, a spirit or demon. From these facts it would seem that elf is from a verb signifying to move, to flow; and älf or elf in Swedish, elv in Danish, is a river, whence Elbe. So spirit is from blowing, a flowing, of air. In Sax. æl is oil and an eel, and ælan is to kindle; all perhaps from the sense of moving, flowing or shooting along. The elf seems to correspond to the demon of the Greeks.]

1. A wandering spirit; a fairy; a hobgoblin; an imaginary being which our rude ancestors supposed to inhabit unfrequented places, and in various ways to affect mankind. Hence in Scottish, elf-shot is an elf-arrow; an arrow-head of flint, supposed to be shot by elfs; and it signifies also a disease supposed to be produced by the agency of spirits. Every elf, and fairy, sprite, / Hop as light as bird from brier. Shak.
2. An evil spirit; a devil. Dryden.
3. A diminutive person. Shenstone.