timer

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. One who keeps or measures and records time; a timekeeper.
2. n. A form of stop-watch for recording or indicating short intervals of time. It shows not actual time, but only relative time, as the time between the beginning and the end of a race, of a trial of speed, etc.

Wiktionary

1. n. Someone or something which times.
2. n. A device used to measure amounts of time.
3. n. Any electronic function that causes a device to be able to do something automatically after a preset amount of time.

GNU Webster's 1913

1. n. A timekeeper; especially, a watch by which small intervals of time can be measured; a kind of stop watch. It is used for timing the speed of horses, machinery, etc.
2. n. (Internal-combustion Engines) In electric ignition, an adjustable device for automatically timing the spark.

WordNet 3.0

1. n. a regulator that activates or deactivates a mechanism at set times
2. n. a timepiece that measures a time interval and signals its end
3. n. (sports) an official who keeps track of the time elapsed