boost·er 
/ˈbu:stɚ/ noun
plural boost·ers /ˈbu:stɚ/ noun [count] 1 : something that boosts someone or something: such as a : an action or substance that makes something stronger or more effective
▪ These exercises are real metabolism boosters. ▪ The herb is said to be an immune booster. [=something that strengthens a person's immunity to illness]
b : something that helps or encourages someone or something
▪ Music is my favorite mood booster. ▪ A sincere compliment can be a true confidence booster.
c : booster shot 2 US : someone who supports an idea or organization
▪ The university has a number of wealthy boosters who contribute generously each year. ▪ the football team's boosters 3 : part of a rocket that provides force for the launch and the first part of the flight
▪ a new design for rocket boosters
▪ These exercises are real metabolism boosters. ▪ The herb is said to be an immune booster. [=something that strengthens a person's immunity to illness]
b : something that helps or encourages someone or something
▪ Music is my favorite mood booster. ▪ A sincere compliment can be a true confidence booster.
c : booster shot
▪ The university has a number of wealthy boosters who contribute generously each year. ▪ the football team's boosters
▪ a new design for rocket boosters
— see also booster seat
