hum /hʌm/ verb (present participle humming, past tense and past participle hummed)
SING [I, T] › to sing without opening your mouth: She hummed to herself as she walked to school. I've forgotten the tune. Can you hum it to me? MAKE SOUND [I] › to make a continuous, low sound: The computers were humming in the background.
be humming › If a place is humming, it is busy and full of activity. hum noun [C] › a low, continuous sound: the hum of traffic