Source : Webster's Revised Unabridged Dictionary (1913)

Hum \Hum\, v. i. [imp. & p. p. {Hummed}; p. pr. & vb. n.
   {Humming}.] [Of imitative origin; cf. G. hummen, D. hommelen.
   [root]15.]
   1. To make a low, prolonged sound, like that of a bee in
      flight; to drone; to murmur; to buzz; as, a top hums. --P.
      Fletcher.

            Still humming on, their drowsy course they keep.
                                                  --Pope.

   2. To make a nasal sound, like that of the letter m
      prolonged, without opening the mouth, or articulating; to
      mumble in monotonous undertone; to drone.

            The cloudy messenger turns me his back, And hums.
                                                  --Shak.

   3. [Cf. {Hum}, interj.] To make an inarticulate sound, like
      h'm, through the nose in the process of speaking, from
      embarrassment or a affectation; to hem.

   4. To express satisfaction by a humming noise.

            Here the spectators hummed.           --Trial of the
                                                  Regicides.

   Note: Formerly the habit of audiences was to express
         gratification by humming and displeasure by hissing.

   5. To have the sensation of a humming noise; as, my head
      hums, -- a pathological condition.

Source : WordNet®

hummed
     See {hum}

hum
     n 1: the state of being or appearing to be actively engaged in an
          activity; "they manifested all the busyness of a pack of
          beavers"; "there is a constant hum of military
          preparation" [syn: {busyness}]
     2: an Islamic fundamentalist group in Pakistan that fought the
        Soviet Union in Afghanistan in the 1980s; now operates as
        a terrorist organization primarily in Kashmir and seeks
        Kashmir's accession by Pakistan [syn: {Harkat-ul-Mujahidin},
         {Harkat ul-Ansar}, {HUA}, {Harkat ul-Mujahedeen}, {Al
        Faran}, {Movement of Holy Warriors}]
     3: a humming noise; "the hum of distant traffic" [syn: {humming}]
     [also: {humming}, {hummed}]

hum
     v 1: sing with closed lips; "She hummed a melody"
     2: be noisy with activity; "This office is buzzing with
        activity" [syn: {buzz}, {seethe}]
     3: sound with a monotonous hum [syn: {thrum}]
     4: make a low continuous sound; "The refrigerator is humming"
     [also: {humming}, {hummed}]