adj. & n.
adj. 1 (usu. attrib.) first in rank or importance; chief (the principal town of the district). 2 main, leading (a principal cause of my success). 3 (of money) constituting the original sum invested or lent.
n. 1 a head, ruler, or superior. 2 the head of some schools, colleges, and universities. 3 the leading performer in a concert, play, etc. 4 a capital sum as distinguished from interest or income. 5 a person for whom another acts as agent etc. 6 (in the UK) a civil servant of the grade below Secretary. 7 the person actually responsible for a crime. 8 a person for whom another is surety. 9 each of the combatants in a duel. 10 a a main rafter supporting purlins. b a main girder. 11 an organ stop sounding an octave above the diapason. 12 Mus. the leading player in each section of an orchestra. principal boy (or girl) an actress who takes the leading male (or female) part in a pantomime. principal clause Gram. a clause to which another clause is subordinate. principal in the first degree a person directly responsible for a crime as its actual perpetrator. principal in the second degree a person directly responsible for a crime as aiding in its perpetration. principal parts Gram. the parts of a verb from which all other parts can be deduced. principalship n.
[ ME f. OF f. L principalis first, original (as PRINCE) ]