boost·er 
(bstər)
(bstər)n.
1. One that boosts, as:
a. A device for increasing power or effectiveness.
b. An enthusiastic promoter, as of a sports team or school.
c. Electronics A radio-frequency amplifier.
d. The primary stage of a multistage rocket that provides the main thrust for launch, liftoff, and initial flight.
2. A booster shot.
3. Slang One who steals goods on display in a store.