noun A hummed tune, i.e. created orally with lips closed.
noun An often indistinct sound resembling human humming.
They could hear a hum coming from the kitchen and found the dishwasher on.
noun Busy activity, like the buzz of a beehive.
noun Unpleasant odour.
noun An imposition or hoax; humbug.
noun A kind of strong drink.
noun A phenomenon, or collection of phenomena, involving widespread reports of a persistent and invasive low-frequency humming, rumbling, or droning noise not audible to all people.