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.

---

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

---

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.

---

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

• 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

Those include a redesigned propellant system on its booster and improved Raptor engines.

From The Wall Street Journal • Apr. 4, 2026

The vaccine is given at eight and 12 weeks, with a booster at one year - Emma confirmed Noa-Rose received all of these.

From BBC • Mar. 26, 2026

The charity has a No Plan B for MenB campaign, aiming to introduce an adolescent booster by 2030 and make the vaccine more affordable on the high street.

From BBC • Mar. 26, 2026

Using a standard booster approach in mice, both vaccine types produced similar antiviral T cell and antibody-producing B cell responses.

From Science Daily • Mar. 17, 2026

When no one was looking, I’d take the food and stick it in a small, hollow space underneath my booster seat.

From "Courage to Soar" by Simone Biles

Related Words

• backer
• enthusiast
• patron
• promoter