Source : Webster's Revised Unabridged Dictionary (1913)

Warble \War"ble\, n.
   A quavering modulation of the voice; a musical trill; a song.

         And he, the wondrous child, Whose silver warble wild
         Outvalued every pulsing sound.           --Emerson.

Warble \War"ble\, n. [Cf. {Wormil}.]
   1. (Far.)
      (a) A small, hard tumor which is produced on the back of a
          horse by the heat or pressure of the saddle in
          traveling.
      (b) A small tumor produced by the larv[ae] of the gadfly
          in the backs of horses, cattle, etc. Called also
          {warblet}, {warbeetle}, {warnles}.

   2. (Zo["o]l.) See {Wormil}.

Warble \War"ble\, v. t. [imp. & p. p. {Warbled}; p. pr. & vb. n.
   {Warbling}.] [OE. werbelen, OF. werbler; of Teutonic origin;
   cf. G. wirbeln to turn, to warble, D. wervelen, akin to E.
   whirl. See {Whirl}.]
   1. To sing in a trilling, quavering, or vibratory manner; to
      modulate with turns or variations; to trill; as, certain
      birds are remarkable for warbling their songs.

   2. To utter musically; to modulate; to carol.

            If she be right invoked in warbled song. --Milton.

            Warbling sweet the nuptial lay.       --Trumbull.

   3. To cause to quaver or vibrate. ``And touch the warbled
      string.'' --Milton.

Warble \War"ble\, v. i.
   1. To be quavered or modulated; to be uttered melodiously.

            Such strains ne'er warble in the linnet's throat.
                                                  --Gay.

   3. To sing in a trilling manner, or with many turns and
      variations. ``Birds on the branches warbling.'' --Milton.

   3. To sing with sudden changes from chest to head tones; to
      yodel.

Source : WordNet®

warble
     n : a lumpy abscess under the hide of domestic mammals caused by
         larvae of a botfly or warble fly

warble
     v 1: sing or play with trills, alternating with the half note
          above or below [syn: {trill}, {quaver}]
     2: sing by changing register; sing by yodeling; "The Austrians
        were yodeling in the mountains" [syn: {yodel}, {descant}]