Principal  —adj. 1 (usu. Attrib.) First in rank or importance; chief. 2 main, leading. —n. 1 chief person. 2 head of some schools, colleges, and universities. 3 leading performer in a concert, play, etc. 4 capital sum as distinct from interest or income. 5 person for whom another is agent etc. 6 civil servant of the grade below secretary. 7 person directly responsible for a crime.  principally adv. [latin: related to *prince]