regulator

noun

1. A device that controls or limits something.
2. (abbreviation, alt-of, ellipsis)A device that controls or limits something.

   “The regulator stopped working and the resulting overvoltage destroyed the device.”

3. A person or group that sets standards of practice, especially regulatory law as sanctioned by statutory law.

   “[…]in part because a key county reservoir had to been^([sic]) drained to reduce earthquake risks highlighted by federal regulators.”

4. A very accurate clock, used by clockmakers to measure the timekeeping of each newly made clock.
5. A gene involved in controlling the expression of one or more other genes.
6. A device that controls the supply of steam to the cylinders of a steam locomotive.

   “Driver G. A. Rowett, of the North Eastern Region's Neville Hill shed, now joined the locomotive as pilotman, and actually took over the regulator, Fireman Wheddon continuing to fire.”

   “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.”

   “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.”

7. (historical)Synonym of bulldozer (“member of intimidating group of white US Southerners”).
8. A positive real number determining the density of the units in Dirichlet's unit theorem.
9. (abbreviation, alt-of)Short for diving regulator.