hum1
  
  v.
 (hums, humming, hummed)
   - make a low, steady continuous sound like that of a bee. 
▸sing with closed lips.
 - informal be in a state of great activity.
 - Brit. informal smell unpleasant.
 
n.
 a low, steady continuous sound. 
▸an unwanted low-frequency noise in an amplifier.
 
  Phrase
  
    
      - hum and haw 
(or chiefly N. Amer. hem and haw)
 Brit. be indecisive. 
    
   
  Derivative
  
  Etymology
  ME: imitative.
 
  
    
hum2
  
  exclam.
 used to express hesitation or dissent.
 
  Etymology
  C16: imitative; rel. to hum1.