Definition of "Starter" :

noun: a culture containing yeast or bacteria that is used to start the process of fermentation or souring in making butter or cheese or dough

"To make sourdough you need a starter."

noun: a hand tool consisting of a rotating shaft with parallel handle

noun: an electric motor for starting an engine

noun: food or drink to stimulate the appetite (usually served before a meal or as the first course)

noun: any new participant in some activity

noun: the official who signals the beginning of a race or competition

noun: a contestant in a team sport who is in the game at the beginning