warble

verb

1. (transitive)To modulate a tone's frequency.
2. (transitive)To sing like a bird, especially with trills.

   “Her voice more sweet than warbling sound, Tho’ sung by nightingale or lark, Her eyes such lustre dart around, Compar’d to them the sun is dark.”

   “In the swamp in secluded recesses, / A shy and hidden bird is warbling a song.”

3. (transitive)To cause to quaver or vibrate.

   “touch the warbled string”

4. (intransitive)To be quavered or modulated; to be uttered melodiously.

   “The wailings of a maiden I recite, / A maiden fair, that Sparabella hight. / Such ſtrains ne'er warble in the linnet's throat, / Nor the gay goldfinch chaunts ſo ſweet a note, [...]”

noun

1. (countable, uncountable)The sound of one who warbles; singing with trills or modulations.

   “The blackbirds and robins and and^([sic]) tits and finches shout at each other, chups and warbles and chirrups that, loosely translated, mean “Fancy a shag?”, “Get OFF my land” or “I’ve got a great big tonker.””

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