Booster definition

(1) An additional dose that makes sure the first dose was effective

(2) The first stage of a multistage rocket

(3) An amplifier for restoring the strength of a transmitted signal

(4) A thief who steals goods that are in a store

(5) Someone who is an active supporter and advocate

(6) A person who backs a politician or a team etc.

"All their supporters came out for the game"

"They are friends of the library"