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English definition of “hum”

hum

verb [I/T]  /hʌm/ (-mm-) us  
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.

hum

noun [C usually sing]  /hʌm/ us  
a continuous, low sound: We could hear the constant hum of traffic outside the window.
(Definition of hum from the Cambridge Academic Content Dictionary © Cambridge University Press)
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