warble

Etymology 1

verb

1. (transitive) To modulate a tone's frequency.
2. (transitive) To sing like a bird, especially with trills.
3. (transitive) To cause to quaver or vibrate.
4. (intransitive) To be quavered or modulated; to be uttered melodiously.

noun

1. The sound of one who warbles; singing with trills or modulations.
2. (military) In naval mine warfare, the process of varying the frequency of sound produced by a narrowband noisemaker to ensure that the frequency to which the mine will respond is covered.

Etymology 2

From Middle English werble (at least for the noun), from Frankish *werbel (mole cricket), cognate to Walloon waerbea.

noun

1. A lesion under the skin of cattle, caused by the larva of a bot fly of genus Hypoderma.
2. A small hard swelling on a horse's back, caused by the galling of the saddle.