humming

Concise Oxford English Dictionary © 2008 Oxford University Press:
hum1

▶verb (hums, humming, hummed)

• 1 make a low, steady continuous sound like that of a bee.

  ■ sing with closed lips.

• 2 informal be in a state of great activity.

• 3 Brit. informal smell unpleasant.

▶noun a low, steady continuous sound.

■ an unwanted low-frequency noise in an amplifier.

– phrases
hum and haw (or chiefly N. Amer. hem and haw) Brit. be indecisive.

– derivatives
hummable adjective,
hummer noun.

– origin ME: imitative.

Concise Oxford English Dictionary © 2008 Oxford University Press:
hum2 (also hmm)

▶exclamation used to express hesitation or dissent.

– origin C16: imitative; rel. to hum1.