principal
prin·ci·pal / ˈprinsəpəl/ • adj. 1. first in order of importance; main: the country's principal cities.2. (of money) denoting an original sum invested or lent: the principal amount of your investment.• n. 1. the person with the highest authority or most important position in an organization, institution, or group: a design consultancy whose principal is based in San Francisco. ∎ the head of a school, college, or other educational institution. ∎ the leading performer in a concert, play, ballet, or opera. ∎ Mus. the leading player in each section of an orchestra.2. a sum of money lent or invested on which interest is paid: the winners are paid from the interest without even touching the principal.3. a person for whom another acts as an agent or representative: stockbrokers in Tokyo act as agents rather than as principals. ∎ Law the person directly responsible for a crime. ∎ hist. each of the combatants in a duel.4. a main rafter supporting purlins.5. an organ stop sounding a main register of open flue pipes typically an octave above the diapason.DERIVATIVES: prin·ci·pal·ship / -ˌship/ n.