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English definition of “hum”

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hum

verb uk   /hʌm/ (-mm-) us  
[I] to make a continuous low sound: The computers were humming in the background. What's that strange humming sound? [I or T] to sing without opening your mouth: She hummed to herself as she walked to school. I've forgotten how that tune goes - could you hum it for me? [I] informal to be busy and full of activity, excitement, sounds, or voices: The bar was really humming last night.

hum

noun [C usually singular] uk   /hʌm/ us  
a continuous low noise: Our house is on a main road, so we can hear the constant hum of traffic. There's an annoying hum on this computer.
(Definition of hum from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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