The term 'BIG PART' can be broken down into two crossword solutions: LEAD (4 letters) and LEADROLE (8 letters). LEAD is a verb that means to guide or direct, while LEADROLE is a noun that refers to the main character or protagonist in a story. Both terms are commonly used in the context of theater, film, and literature, where the LEAD character is the one who drives the plot forward. In other contexts, such as business or politics, the term 'LEAD' can also refer to someone who is in charge or has authority over others.