regulator

(rĕgˈyə-lāˌtər)

1. One that regulates, as:
   a. The mechanism in a watch by which its speed is governed.
   b. A highly accurate clock used as a standard for timing other clocks.
   c. A device used to maintain uniform speed in a machine; a governor.
   d. A device used to control the flow of gases, liquids, or electric current.
2. One, such as the member of a governmental regulatory agency, that ensures compliance with laws, regulations, and established rules: banking regulators; price regulators.
3. A substance that affects the amount of product or the progress of a biochemical reaction or process: a regulator of embryogenesis.
4. See regulator gene.