bum1
  
  n.
 Brit. informal a person's buttocks or anus.
 
  Etymology
  ME: of unknown origin.
 
  
    
bum2
  
  n.
 N. Amer.   - a vagrant.
 - a lazy or worthless person.
 - a devotee of a particular activity:
 a ski bum.
 
v.
 (bums, bumming, bummed)
   - get by asking or begging.
 - 
(bum around)
 chiefly N. Amer. pass one's time idly.
 - 
(usu. be bummed out)
 N. Amer. make (someone) feel upset or disappointed.
 
adj.
 bad; wrong:
 not one bum note was played.
 
  Phrase
  
    
      - give someone the bum's rush
 chiefly N. Amer. forcibly eject someone. 
    
   
  Etymology
  C19: prob. from bummer.