warble (v.)

late 14c., from Old North French werbler "to sing with trills and quavers" (Old French guerbloiier), from Frankish *werbilon (cognate with Old High German wirbil "whirlwind," German Wirbel "whirl, whirlpool, tuning peg, vertebra," Middle Dutch wervelen "to turn, whirl"); see whirl (v.). Related: Warbled; warbling. The noun is recorded from late 14c.

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Definitions of warble from WordNet
warble (v.)
sing or play with trills, alternating with the half note above or below;
Synonyms: trill / quaver
warble (v.)
sing by changing register; sing by yodeling;
Synonyms: yodel / descant
warble (n.)
a lumpy abscess under the hide of domestic mammals caused by larvae of a botfly or warble fly;