hum

Hum is defined as to make a low, steady sound like a motor, to be busy, or to sing with closed lips.

(verb)

When a fan whirs quietly in the background, this is an example of when the fan hums.
When a cafeteria has a low, steady sound of chatter, this is an example of when the cafeteria hums.
When you make "hmmm.... hmmmm... hmmmm" sounds to the beat of a song, singing without opening your lips, this is an example of when you hum.

The definition of a hum is a low, steady sound.

(noun)

The quiet whirring of a fan in the background is an example of a hum.
The small, steady noise your speakers make when your amp is acting up is an example of a hum.

See hum in Webster's New World College Dictionary

intransitive verb hummed, humming

Origin: ME hummen, of echoic orig., as in Ger hummel, bumblebee, MDu hommeln, hum

transitive verb

noun

Related Forms:

interjection, noun

hem

intransitive verb hummed, humming

hem

See hum in American Heritage Dictionary 4

verb hummed hummed, hum·ming, hums

verb, intransitive

a. To emit a continuous low droning sound like that of the speech sound (m) when prolonged.
b. To emit the continuous droning sound of a bee on the wing; buzz.
c. To give forth a low continuous drone blended of many sounds: The avenue hummed with traffic.
To be in a state of busy activity.
To produce a tune without opening the lips or forming words.

verb, transitive