1. A heavy-rimmed rotating wheel used to minimize variations in angular velocity and revolutions per minute, as in a machine subject to fluctuation in drive and load.
2. An analogous device, especially one used to regulate the speed of clockwork.

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.