regulator

Etymology

regulate + -or.

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.
   […]in part because a key county reservoir had to been drained to reduce earthquake risks highlighted by federal regulators. 15 June 2021, Suzanne Rust, “A problem Silicon Valley can’t solve: Drought, quake risk”, in Los Angeles Times, Nant Capital, LLC
3. A very accurate clock, used by clockmakers to measure the timekeeping of each newly made clock.
4. (genetics) A gene involved in controlling the expression of one or more other genes.
5. (rail transport) A device that controls the supply of steam to the cylinders of a steam locomotive.
   To start No. S.002 effectively with a heavy train, one opens the main regulator sufficiently to move the train off very slowly. An excess of regulator opening with the by-pass valve open can cause heavy slipping; if the worst happens, the slipping continues a little longer after the regulator is closed than on an English locomotive. 1961 March, Balmore, “Driving and firing modern French steam locomotives”, in Trains Illustrated, page 146
   This uncoupling done, Gimbert opened the regulator as Nightall climbed back onto the footplate, in order to pull the one burning wagon away from the rest of the bomb-laden train. January 12 2022, Benedict le Vay, “The heroes of Soham...”, in RAIL, number 948, page 42
6. (historical) A bulldozer (member of intimidating group of white US Southerners).