<p><strong>Noun</strong></p><ul><li>a person or thing that boosts, especially an energetic and enthusiastic supporter.</li><li>Electricity: a device connected in series with a current for increasing or decreasing the nominal circuit voltage.</li><li>Railroads: any machine, device, phenomenon, etc., that helps to move a train, as a tailwind, downgrade, roller bearings, or especially a helper locomotive.</li><li>Military: an explosive more powerful than a primer, for ensuring the detonation of the main charge of a shell.</li><li>Rocketry: a rocket engine used as the principal source of thrust in the takeoff of a rocket or missile.</li><li>Medicine/Medical: also called booster dose, a dose of an immunizing substance given to maintain or renew the effect of a previous one.</li><li>Pharmacology: a chemical compound, medicinal substance, or the like, that serves as a synergist.</li><li>a radio-frequency amplifier for connecting between a radio or television antenna and the receiving set to intensify the received signal.</li><li>an auxiliary pump, used in a pipeline or other system, to add to or maintain a prevailing amount of pressure or vacuum.</li><li>Slang: a shoplifter or petty thief.</li></ul>