hum

Etymology

From Middle English hummen (“to hum, buzz, drone, make a murmuring sound to cover embarrassment”); akin to Dutch hommelen (“to bumble, buzz”), dialectal Dutch hommen (“to buzz, hum”), Middle High German hummen (“to hum”), probably ultimately of imitative origin.

noun

1. A hummed tune, i.e. created orally with lips closed.
2. An often indistinct sound resembling human humming.
   They could hear a hum coming from the kitchen, and found the dishwasher on.
3. Busy activity, like the buzz of a beehive.
4. (UK, slang) Unpleasant odour.
5. (dated) An imposition or hoax; humbug.
6. (obsolete) A kind of strong drink.
7. (with article) 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.
   There is a range of theories from farm or factory machinery to conspiracy theories such as flying saucers. And yet, "the hum" remains an unsolved case. 2011-06-13, “Who, What, Why: Why is 'the hum' such a mystery?”, in BBC News

verb

1. (intransitive) To make a sound from the vocal chords without pronouncing any real words, with one's lips closed.
   We are humming happily along with the music.
2. (transitive) To express by humming.
   to hum a tune
   The team ominously hummed “We shall overcome” as they came back onto the field after the break.
3. (intransitive) To drone like certain insects naturally do in motion, or sounding similarly
4. (intransitive) To buzz, be busily active like a beehive
   The streets were humming with activity.
5. (intransitive) To produce low sounds which blend continuously
6. (Britain, slang) To reek, smell bad.
   This room really hums — have you ever tried spring cleaning, mate?
7. (transitive, UK, dated, slang) To flatter by approving; to cajole; to deceive or impose upon; to humbug.

intj

1. Synonym of hmm: a noise indicating thought, consideration, &c.
2. Synonym of um: a noise indicating doubt, uncertainty, &c.