booster

American  

[boo-ster] / ˈbu stər /

noun

1. a person or thing that boosts, especially an energetic and enthusiastic supporter.

2. Electricity. a device connected in series with a current for increasing or decreasing the nominal circuit voltage.

3. Railroads. any machine, device, phenomenon, etc., that helps to move a train, as a tailwind, downgrade, roller bearings, or especially a helper locomotive.

4. Military. an explosive more powerful than a primer, for ensuring the detonation of the main charge of a shell.

5. Rocketry.

   1. a rocket engine used as the principal source of thrust in the takeoff of a rocket or missile.

   2. 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.

6. Also called booster shot.  Also called booster dose,.  Medicine/Medical. a dose of an immunizing substance given to maintain or renew the effect of a previous one.

7. Pharmacology. a chemical compound, medicinal substance, or the like, that serves as a synergist.

8. a radio-frequency amplifier for connecting between a radio or television antenna and the receiving set to intensify the received signal.

9. an auxiliary pump, used in a pipeline or other system, to add to or maintain a prevailing amount of pressure or vacuum.

10. Slang. a shoplifter or petty thief.

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booster British  

/ ˈbuːstə /

noun

1. a person or thing that supports, assists, or increases power or effectiveness

2. Also called: launch vehicle.  the first stage of a multistage rocket

3. radio television

   1. a radio-frequency amplifier connected between an aerial and a receiver to amplify weak incoming signals

   2. a radio-frequency amplifier that amplifies incoming signals, retransmitting them at higher power

4. another name for supercharger

5. short for booster dose

6. slang a shoplifter

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booster Scientific  

/ bo̅o̅′stər /

1. 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.

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Usage

What is a booster shot? A booster shot is an additional dose of a vaccine given to a person in order to maintain or renew the effect of a previous dose. This is sometimes called a booster dose (especially since vaccines aren’t always given via shots) or simply a booster. Vaccines strengthen the body’s immunity against disease. They work by introducing a killed, weakened, or otherwise modified version of a specific disease (such as a virus or bacterium) so that the body’s immune system will produce antibodies that will destroy those specific pathogens if they ever enter the body again. A booster shot basically refreshes the immune system’s memory of a disease in order to strengthen immunity—it “boosts” the existing defenses. Booster shots are commonly given to both children and adults. Common vaccines that typically involve one or multiple booster shots include those against tetanus, hepatitis A, human papillomavirus (HPV), and measles, mumps, and rubella (MMR). The timing of the booster shot varies depending on the vaccine—some are given a few months after the initial dose, while others are given years later. Medical organizations such as the Centers for Disease Control and Prevention (CDC) provide immunization schedules that recommend the frequency of booster shots.

Other Word Forms

Derived Forms

• boosterish
  adjective

Etymology

Origin of booster

An Americanism dating back to 1885–90; boost + -er ¹

Explanation

If you’re a big fan and promoter of something or someone, you're a booster. Go team! A booster provides support, like a kid’s booster seat, a follow-up dose of medicine, or a booster rocket that launches the Space Shuttle. Boosters of teams, groups, or organizations often form official clubs to coordinate their fundraising and event planning. Another kind of booster is an engine or rocket that's the first stage of launching a space vehicle into orbit. And in medicine, a booster is a second (or subsequent) dose of a vaccine that helps the initial dose work better. All of these boosters assist, encourage, or boost in some way.

Example Sentences

Additionally, the “Never Tell Me the Odds” booster and three second-stage vehicles that were on site also appear to be in good shape, he said.

From MarketWatch • Jun. 2, 2026

Most neighborhood police stations now have their own dedicated booster organizations.

From Los Angeles Times • May 28, 2026

The Federal Aviation Administration said SpaceX must conduct an investigation into why the booster didn’t perform as expected during the company’s test flight last Friday before it can launch its Starship rocket again.

From The Wall Street Journal • May 27, 2026

Authorities are urging affected communities to update their vaccinations, especially teenagers and adults who need to get booster shots.

From BBC • May 26, 2026

“Lose two games by two points and they’re ready to hang ’im,” he said quietly at the booster club meeting that Tuesday night following the loss to the Rebels.

From "Friday Night Lights: A Town, A Team, And A Dream" by H.G. Bissinger

Related Words

• backer
• enthusiast
• patron
• promoter