1. One who keeps track of time; a timekeeper.
2. A timepiece, especially one used for measuring and signaling the end of time intervals, as on a stove.
3. A switch or regulator that controls or activates and deactivates another mechanism at set times.
4. A device that controls the timing of the sparks that ignite the fuel in an internal-combustion engine.

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.