hum
verb uk/hʌm/ us/hʌm/ -mm-
(MAKE A NOISE)
[ I ]发出连续低沉的声音，嗡嗡作响
to make a continuous low sound
The computers were humming in the background. 计算机在背景中嗡嗡作响。
What's that strange humming sound? 那种奇怪的嗡嗡声是什么？
[ I or T ]哼（曲子）
to sing without opening your mouth
She hummed to herself as she walked to school. 她在上学的路上边走边哼曲子。
I've forgotten how that song goes - could you hum it for me? 我忘了那个调子怎么唱了——你能给我哼一下吗？
[ I ] informal忙乱，忙碌;嘈杂
to be busy and full of activity, excitement, sounds, or voices
The bar was really humming last night. 昨晚酒吧里一片乱哄哄的。
Idiom
hum and hawidiom UK (US hem and haw) （长时间）犹豫不决
to be uncertain and take a long time deciding something
We hummed and hawed for months before actually deciding to buy the house. 在真正决定买这所房子之前，我们犹豫了数月之久。
hum
noun [ C usually singular ] uk/hʌm/ us/hʌm/
持续低沉的噪音;嗡嗡声
a continuous low noise
Our house is on a main road, so we can hear the constant hum of traffic. 我们的房子在大路旁，所以能听见持续不断的交通噪声。
There's an annoying hum on this computer. 这台计算机总是发出一种让人心烦的嗡嗡声。