To warble means to sing with a gentle, flowing sound that moves up and down in pitch, like a bird trilling in the morning. When birds warble, their songs ripple and quiver with quick changes in tone. Warblers are a family of small songbirds named for exactly this quality: their voices flutter and roll in beautiful, complex patterns.

Singers can warble too. When a vocalist warbles a melody, their voice rises and falls smoothly, sometimes with a slight trembling quality. You might hear someone warble a lullaby or warble along with the radio in the car. The word often suggests something sweet and musical, though not necessarily powerful or loud.

As a noun, a warble is a song or sound like this. The word can also describe sounds that resemble birdsong, like when someone's voice warbles because they're nervous or emotional. If you've ever heard your own voice shake a bit while speaking in front of the class, that's a kind of warbling. Less commonly, warble can refer to a soft, bubbling sound, like water trickling over stones in a stream.