Regulator

noun

1. A device that controls or limits something.

   "The voltage regulator stopped working and the resulting overload destroyed the device."

2. A person or group that sets standards of practice, especially those established by law.
3. A very accurate clock, used by clockmakers to measure the timekeeping of each newly made clock.
4. A gene involved in controlling the expression of one or more other genes.
5. A device that controls the supply of steam to the cylinders of a steam locomotive.