booster - definition and synonyms

noun [countable] 

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  1. 1
    something that makes you feel more confident, more healthy etc

    Fruit is an excellent health booster.

    confidence/morale booster:

    A new haircut can be a great confidence booster.

  2. 2
    medical a small extra amount of a medical drug that you are given so that a drug you had before will continue to be effective

    a tetanus booster