- 1a thing that helps, encourages, or improves someone or something a morale/confidence booster
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- 2an extra small amount of a drug that is given to increase the effect of one given earlier, for example to protect you from a disease for longer a tetanus booster
- 3a person who gives their support to someone or something, especially in politics a meeting of Republican boosters
- 4(also booster rocket) a rocket that gives a spacecraft extra power when it leaves the earth, or that makes a missile go further
- 5a device that gives extra power to a piece of electrical equipment
Check pronunciation: booster