Real Dictionary

warble
verb: If someone warbles, they sing in a high-pitched, rather unsteady voice.
verb: When a bird warbles, it sings pleasantly.

warble in American English 1
the act of warbling
to sing (a song, notes, etc.) melodiously, with trills, quavers, runs, etc., as a bird does
to sing melodiously, with trills, etc.
intransitive verb: to sing or whistle with trills, quavers, or melodic embellishments
noun: a warbled song or succession of melodic trills, quavers, etc
transitive verb: to sing (an aria or other selection) with trills, quavers, or melodious turns

warble in American English 2
a small, hard tumor on the back of a horse, caused by the rubbing and pressing of a saddle
noun: a small, hard tumor on a horse's back, produced by the galling of the saddle

warble in British English 1
verb: to sing (words, songs, etc) with trills, runs, and other embellishments

warble in British English 2
noun: a small lumpy abscess under the skin of cattle caused by infestation with larvae of the warble fly