hum

sing, hum

这两个动词均含“唱”之意。
sing: 普通用词，泛指一般的歌唱或发出悦耳的声音。
hum: 指闭着双唇而不唱出字来，低语般的哼唱。

名词 hum:

1. the state of being or appearing to be actively engaged in an activity
   同义词：busyness
2. an Islamic fundamentalist group in Pakistan that fought the Soviet Union in Afghanistan in the 1980s; now operates as a terrorist organization primarily in Kashmir and seeks Kashmir's accession by Pakistan
   同义词：Harkat-ul-Mujahidin, Harkat ul-Ansar, HUA, Harkat ul-Mujahedeen, Al Faran, Movement of Holy Warriors
3. a humming noise
   同义词：humming

动词 hum:

1. sing with closed lips
2. be noisy with activity
   同义词：buzz, seethe
3. sound with a monotonous hum
   同义词：thrum
4. make a low continuous sound

1. His strong voice cut through the hum of conversation like a knife through butter.
   他那宏亮有力的声音一下子压倒了嗡嗡的谈话声。
2. Hum the opening bars of your favourite tune.
   哼一哼你喜爱的曲子的开头几个小节。
3. Hum, you're joking!
   哼，你在开玩笑吧！
4. She was humming to herself.
   她独自哼着歌。
5. She continued to hum the song over and over.
   她一遍又一遍地不断哼唱那支歌。
6. The only sound he heard was the hum of the machine.
   他听到的唯一的声音就是那台机器的嗡嗡声。

hum

v.（动词）
hummed,hum.ming,hums
v.intr.（不及物动词）

To emit a continuous low droning sound like that of the speech sound (m) when prolonged.
嗡嗡声，哼哼声：发出一种持续、低沉的嗡嗡声，类似m被拖长后的声音
To emit the continuous droning sound of a bee on the wing; buzz.
发嗡嗡声：蜜蜂翅膀发出的持续的嗡嗡声；嗡嗡声
To give forth a low, continuous drone blended of many sounds:
发出嘈杂声：发出各种持续、低沉、混在一起的嗡嗡声：
例句：
The avenue hummed with traffic.
大路上的车辆发出混杂的声音

To be in a state of busy activity.
忙碌：处于繁忙的状态
To produce a tune without opening the lips or forming words.
哼：不张开嘴或不构成词而产生的声调
v.tr.（及物动词）
To sing (a tune) without opening the lips or forming words.
哼唱：不张开嘴或不构成词而唱（曲调）
n.（名词）
The sound produced by humming.
嗡嗡声：哼出来的声音
The act of humming.
哼唱的动作
interj.（感叹词）
Used to indicate hesitation, surprise, or displeasure.
发哼哼声：用于表示犹豫，吃惊或不快

来源：
Middle English hummen
中古英语 hummen
[of imitative origin]
[源于模仿]

【引伸】
hum.mable
adj.（形容词）
hum.mer
n.（名词）