boost ‧ er /ˈbuːstə $ -ər/ BrE AmE noun [countable]
1 . a small quantity of a drug that increases the effect of one that was given before, so that someone continues to be protected against a disease:
a booster shot
2 . something that helps someone or something to increase or improve, or to be more successful or confident:
a booster pump
a profit booster for the company
morale/confidence booster
Mail from home is a big morale booster for faraway troops.
3 . a rocket that is used to provide extra power for a ↑ spacecraft to leave the Earth:
a giant booster rocket
4 . American English someone who gives a lot of support to a person, organization, or idea:
a dance organized by the school’s booster club