booster

noun

• 1a device for increasing electrical voltage or signal strength.

• 2the first stage of a rocket or spacecraft, used to give initial acceleration and then jettisoned.

• 3 Medicine a dose of a vaccine that increases or renews the effect of an earlier one: boosters at five-year intervals are recommended [as modifier]:a booster injection

• 4 [in combination] a source of help or encouragement:job fairs are a great morale booster
• North American a keen promoter of a person, organization, or cause.

• 5North American informal a shoplifter.