Booster

a person or thing that boosts, especially an energetic and enthusiastic supporter.
Electricity. a device connected in series with a current for increasing or decreasing the nominal circuit voltage.
Railroads. any machine, device, phenomenon, etc., that helps to move a train, as a tailwind, downgrade, roller bearings, or especially a helper locomotive.
Military. an explosive more powerful than a primer, for ensuring the detonation of the main charge of a shell.
Rocketry.

a rocket engine used as the principal source of thrust in the takeoff of a rocket or missile.
the first stage containing this engine and its fuel supply, which may or may not be detached from the rocket when the fuel has been consumed.

Medicine/Medical. Also called booster dose, booster shot. a dose of an immunizing substance given to maintain or renew the effect of a previous one.
Pharmacology. a chemical compound, medicinal substance, or the like, that serves as a synergist.
a radio-frequency amplifier for connecting between a radio or television antenna and the receiving set to intensify the received signal.
an auxiliary pump, used in a pipeline or other system, to add to or maintain a prevailing amount of pressure or vacuum.
Slang. a shoplifter or petty thief.
Contemporary Examples

Families Decry Supreme Court Decision on Juvenile Life Without Parole Michael Daly June 25, 2012
Time to Kill Miami Football Buzz Bissinger August 18, 2011
Squishes, Step Aside: Ted Cruz and Chris Christie’s Old-School Manliness Michelle Cottle May 12, 2013
Great Weekend Reads The Daily Beast July 2, 2011
Jenny McCarthy Says She’s Never Been Anti-Vaccine. Yeah, Right. Russell Saunders April 15, 2014

Historical Examples

Glory of Youth Temple Bailey
The Big Tomorrow Paul Lohrman
A Yankee Flier with the R.A.F. Rutherford G. Montgomery
Masters of Space Edward Elmer Smith
Perfect Control Richard Stockham

noun
a person or thing that supports, assists, or increases power or effectiveness
Also called launch vehicle. the first stage of a multistage rocket
(radio, television)

a radio-frequency amplifier connected between an aerial and a receiver to amplify weak incoming signals
a radio-frequency amplifier that amplifies incoming signals, retransmitting them at higher power

another name for supercharger
short for booster dose
(slang, mainly US) a shoplifter
n.
booster
(b’stər)
An additional dose of an immunizing agent, such as a vaccine or toxoid, given at a time period of weeks to years after the initial dose to sustain the immune response elicited by the first dose. Tetanus, diphtheria, and measles vaccines are commonly given in booster doses.

A shoplifter; pilferer: Got a booster for you. The chunky girl in blue at the lace counter/ He knew they couldn’t be boosters or creepers (1908+)
A huckster’s or auctioneer’s assistant who pretends to buy in order to stimulate others; shill (1905+ Carnival)
A person who praises extravagantly; fan (1890+)

A data-parallel language.
“The Booster Language”, E. Paalvast, TR PL 89-ITI-B-18, Inst voor Toegepaste Informatica TNO, Delft, 1989.