That produces or emits a continuous steady deep humming or buzzing sound; (of sound) monotonous, deep, and sustained.

Characterized by a continuous steady deep humming or buzzing sound, or a monotonous, dull tone.

(Of a sound, utterance, etc.) continuing on or repeating the same note; having little or no variation in tone or pitch; (of a musical instrument)…

Of a sound or utterance: continuing on or repeating the same note; having little or no variation in tone, pitch, or cadence. Also, of a musical…

Having no distinctive quality; (a) of sound: without modulation or expression; (b) of colour: dull.

Uttered or emitted monotonously; characterized by, or of the nature of, a low, continuous sound. Also with out.

Sounding like a strummed instrument.