the hydraulic pump of an automotive braking system that contains a cylinder and one or two pistons, is actuated by the brake pedal, and supplies hydraulic fluid under pressure to the brakes at each wheel.
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British Dictionary definitions for master cylinder
a large cylinder in a hydraulic system in which the working fluid is compressed by a piston enabling it to drive one or more slave cylinders: See also slave cylinder
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012