One who holds a position of presiding rank, especially the head of an elementary school or high school. First, highest, or foremost in importance, rank, worth, or degree; chief. See Synonyms at chief. Of, relating to, or being financial principal, or a principal in a financial transaction. A main participant in a situation. A person having a leading or starring role. The capital or main body of an estate or financial holding as distinguished from the interest or revenue from it. A sum of money owed as a debt, upon which interest is calculated. Law A person who empowers another to act as his or her representative. Law The person having prime responsibility for an obligation as distinguished from one who acts as surety or as an endorser. Law One who commits or is an accomplice to a crime. Architecture Either of a pair of inclined timbers forming the sides of a triangular truss for a pitched roof.