booster

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that boosts, as.
• noun A device for increasing power or effectiveness.
• noun An enthusiastic promoter, as of a sports team or school.
• noun Electronics A radio-frequency amplifier.
• noun The primary stage of a multistage rocket that provides the main thrust for launch, liftoff, and initial flight.
• noun A booster shot.
• noun Slang One who steals goods on display in a store.

from The Century Dictionary.

• noun One who boosts.
• noun In electricity, a device by which the electromotive force in an electric circuit is regulated.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Elec.) 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.
• noun an enthusiastic supporter.
• noun 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.
• noun (Med.) 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.
• noun any auxiliary device or part of a device to provide increased power, force, or effectiveness, as with a pumping device.
• noun (Mil.) 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Something that boosts.
• noun The first stage of a multistage rocket that provides the thrust for liftoff and the initial flight
• noun Someone who is a fan or supporter of something.
• noun Someone who promotes a town or business
• noun A member of a booster club.
• noun A booster dose.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a person who backs a politician or a team etc.
• noun the first stage of a multistage rocket
• noun an additional dose that makes sure the first dose was effective
• noun someone who is an active supporter and advocate
• noun a thief who steals goods that are in a store
• noun an amplifier for restoring the strength of a transmitted signal