Source : Webster's Revised Unabridged Dictionary (1913)

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.

            Every elf, and fairy sprite, Hop as light as bird
            from brier.                           --Shak.

   2. A very diminutive person; a dwarf.

   {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.

Elf \Elf\, v. t.
   To entangle mischievously, as an elf might do.

         Elf all my hair in knots.                --Shak.

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

            He seemeth elvish by his countenance. --Chaucer.

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

Source : WordNet®

elf
     n 1: (folklore) fairies that are somewhat mischievous [syn: {hob},
           {gremlin}, {pixie}, {pixy}, {brownie}, {imp}]
     2: below 3 kilohertz [syn: {extremely low frequency}]
     [also: {elves} (pl)]

Source : Free On-Line Dictionary of Computing

ELF
     
        Binary format used by System V Release 4 Unix.