1. Slang. An adverse reaction to a hallucinogenic drug.
2. Slang. One that depresses, frustrates, or disappoints: Getting stranded at the airport was a real bummer.
3. 1. A loafer or idler.
   2. A beggar.

[From BUM¹, adj.. Sense 3, probably from German Bummler, loafer, from bummeln, to loaf.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.