hum

/hʌm/ v [I/T] (-mm-)

Definition

› to make a continuous, low sound, or to sing a tune with closed lips: [I] Debbie always hums to herself when she listens to music. [T] I’ve forgotten how that tune goes – could you hum it for me? › fig. If something is humming, it is very busy and full of activity: [I] Factories that make paper products are humming at 97% of capacity.

(Definition of hum v from the Cambridge Academic Content Dictionary © Cambridge University Press)