The Collaborative International Dictionary of English v.0.48:

Elves \Elves\, n.; pl. of Elf.
   [1913 Webster] Elvish \Elv"ish\, a.
   1. Pertaining to elves; implike; mischievous; weird; also,
      vacant; absent in demeanor. See Elfish.
      [1913 Webster]

            He seemeth elvish by his countenance. --Chaucer.
      [1913 Webster]

   2. Mysterious; also, foolish. [Obs.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Elf \Elf\ ([e^]lf), n.; pl. Elves ([e^]lvz). [AS. [ae]lf, ylf;
   akin to MHG. alp, G. alp nightmare, incubus, Icel. [=a]lfr
   elf, Sw. alf, elfva; cf. Skr. [.r]bhu skillful, artful, rabh
   to grasp. Cf. Auf, Oaf.]
   1. An imaginary supernatural being, commonly a little sprite,
      much like a fairy; a mythological diminutive spirit,
      supposed to haunt hills and wild places, and generally
      represented as delighting in mischievous tricks.
      [1913 Webster]

            Every elf, and fairy sprite,
            Hop as light as bird from brier.      --Shak.
      [1913 Webster]

   2. A very diminutive person; a dwarf.
      [1913 Webster]

   Elf arrow, a flint arrowhead; -- so called by the English
      rural folk who often find these objects of prehistoric
      make in the fields and formerly attributed them to
      fairies; -- called also elf bolt, elf dart, and elf
      shot.

   Elf child, a child supposed to be left by elves, in room of
      one they had stolen. See Changeling.

   Elf fire, the ignis fatuus. --Brewer.

   Elf owl (Zo["o]l.), a small owl (Micrathene Whitneyi) of
      Southern California and Arizona.
      [1913 Webster]

WordNet (r) 3.0 (2006):

elves
    n 1: an acronym for emissions of light and very low frequency
         perturbations due to electromagnetic pulse sources;
         extremely bright extremely short (less than a msec)
         electrical flashes forming a huge ring (up to 400 km
         diameter) in the ionosphere