GNU Collaborative International Dictionary of English

Found one definition

1.       
   bummer (bŭmˈẽr), n.
   1. An idle, worthless fellow, who is without any visible means of support; a loafer; a dissipated sponger; one who bums. [Slang, U.S.]
   
   [1913 Webster]
   
   
   2. an unpleasant event, experience, or situation; as, “getting caught in a cloudburst while wearing my best suit was a bummer”.  [Slang, U.S.]
   
   [PJC]