[1] : The Collaborative International Dictionary of English v.0.48

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.
   1913 webster
   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.
      1913 webster

   2. to utter musically; to modulate; to carol.
      1913 webster

            if she be right invoked in warbled song. --milton.
      1913 webster

            warbling sweet the nuptial lay.       --trumbull.
      1913 webster

   3. to cause to quaver or vibrate. "and touch the warbled
      string." --milton.
      1913 webster
see also:
warbled warbling whirl 

[2] : Moby Thesaurus II by Grady Ward, 1.0

25 moby thesaurus words for "warbling":
   bel canto, bravura, choral singing, coloratura, croon, crooning,
   folk singing, hum, humming, intonation, lyricism, operatic singing,
   scat, scat singing, singing, sol-fa, sol-fa exercise, solfeggio,
   solmization, song, tonic sol-fa, vocal music, vocalization, yodel,
   yodeling

Warbling >> W Words
Warbling, definition of term: Warbling
warbling_pag1.html