n Something that boosts.
n The first stage of a multistage rocket that provides the thrust for liftoff and the initial flight.
n A motor-generator set used for voltage regulation in direct current electrical power circuits.
n Someone who is a fan or supporter of something.
n Someone who promotes a town or business.
n A member of a booster club.
n (immunology) A booster dose.
n (explosives) A small quantity of a sensitive explosive that is triggered by a detonator and provides the energy needed to detonate a larger quantity of a less-sensitive explosive.
n (linguistics) A term that serves to amplify or strengthen an utterance, such as "really".
n (video games) A power-up item.
n (gaming) A package of cards or figurines designed to add to a player's collection.
n (slang) A thief.
n (rail transport) A booster engine fitted to a steam locomotive.
v (transitive, medicine) To give a booster shot to; to boost.
n Short for booster seat. [A child safety seat that raises the vertical position of the user to allow a safer use of regular car seat belts.]