noun

• A device that controls or limits something.
• A person or group that sets standards of practice, especially those established by law.
• A very accurate clock, used by clockmakers to measure the timekeeping of each newly made clock.
• (genetics) A gene involved in controlling the expression of one or more other genes.
• (rail transport) A device that controls the supply of steam to the cylinders of a steam locomotive.
• (historical) A bulldozer (member of intimidating group of white US Southerners).