The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster] Yodel

The Collaborative International Dictionary of English v.0.48:

Yodel \Yo"del\, Yodle \Yo"dle\, n.
   A song sung by yodeling, as by the Swiss mountaineers.
   [1913 Webster]

WordNet (r) 3.0 (2006):

yodel
    n 1: a songlike cry in which the voice fluctuates rapidly
         between the normal voice and falsetto
    v 1: sing by changing register; sing by yodeling; "The Austrians
         were yodeling in the mountains" [syn: yodel, warble,
         descant]

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "yodel":
   anthem, ballad, bel canto, bravura, carol, chant, chirp, chirrup,
   choir, choral singing, chorus, coloratura, croon, crooning,
   descant, do-re-mi, folk singing, hum, humming, hymn, intonate,
   intonation, intone, lilt, lyricism, minstrel, operatic singing,
   pipe, psalm, quaver, roulade, scat, scat singing, serenade, shake,
   sing, sing in chorus, singing, sol-fa, sol-fa exercise, solfeggio,
   solmizate, solmization, song, tonic sol-fa, tremolo, trill, troll,
   tweedle, tweedledee, twit, twitter, vocal music, vocalization,
   vocalize, warble, warbling, whistle, yodeling