n. An instrument for regulating the electro-motive force in an alternating-current circuit; -- so called because used to “boost”, or raise, the pressure in the circuit.n. an enthusiastic supporter.n. the first stage of a multistage rocket, providing all or part of the driving force at lift-off and until the second stage ignites, whether or not the booster stage is detached after the fuel is spent. Also called booster rocket. In some cases, a booster has been used to assist the takeoff of airplanes.n. an immunizing medication given after an initial immunizing treatment, to provide increased or extended immunity. Also called booster dose. When in the form of an injection, it may be called a booster shot.n. any auxiliary device or part of a device to provide increased power, force, or effectiveness, as with a pumping device.n. an explosive charge which is more powerful than a primer, used in conjunction with a primer to assure detonation of the main charge. Integrated blasting caps containing separate compartments for primer and booster are used as detonators for certain explosives.