"humming" in the noun sense

1. hum, humming

a humming noise

"the hum of distant traffic"

2. humming

the act of singing with closed lips

"humming" in the verb sense

1. hum

sing with closed lips

"She hummed a melody"

2. hum, buzz, seethe

be noisy with activity

"This office is buzzing with activity"

3. hum, thrum

sound with a monotonous hum

4. hum

make a low continuous sound

"The refrigerator is humming"

Source: WordNet® (An amazing lexical database of English)

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