1. One that deadens, restrains, or depresses: Rain put a damper on our picnic plans.
2. An adjustable plate, as in the flue of a furnace or stove, for controlling the draft.
3. Music.
   1. A device in various keyboard instruments for deadening the vibrations of the strings.
   2. A mute for various brass instruments.
4. A device that eliminates or progressively diminishes vibrations or oscillations, as of a magnetic needle.

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.