DuckCorp Dico

Found one definition

1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   bum \bum\, v. i. [imp. & p. p. bummed; p. pr. & vb. n.
      bumming (?).] [See Boom, v. i., to roar.]
      To make murmuring or humming sound. --Jamieson.
      [1913 Webster]
      to bum around to wander about idly or aimlessly.
         [PJC]