Source : Webster's Revised Unabridged Dictionary (1913)

Yodel \Yo"del\, Yodle \Yo"dle\, v. t. & i. [imp. & p. p.
   {Yodeled}, {Yodled}; p. pr. & vb. n. {Yodeling}, {Yodling}.]
   [G. jodeln.]
   To sing in a manner common among the Swiss and Tyrolese
   mountaineers, by suddenly changing from the head voice, or
   falsetto, to the chest voice, and the contrary; to warble.

Yodel \Yo"del\, Yodle \Yo"dle\, n.
   A song sung by yodeling, as by the Swiss mountaineers.

Source : WordNet®

yodel
     n : a songlike cry in which the voice fluctuates rapidly between
         the normal voice and falsetto
     v : sing by changing register; sing by yodeling; "The Austrians
         were yodeling in the mountains" [syn: {warble}, {descant}]
     [also: {yodelling}, {yodelled}]