principal

adjective

• 1first in order of importance; main:the country’s principal cities

• 2denoting an original sum invested or lent:the principal amount of your investment

noun

• 1the most important or senior person in an organization or group:a design consultancy whose principal is based in San Francisco
• the head of a school, college, or other educational institution: I was appointed principal of the new school
• the leading performer in a concert, play, ballet, or opera: the singing style of the principals
• Music the leading player in each section of an orchestra: he had been an outstanding principal in the orchestra
• (in certain professions) a fully qualified practitioner: principals in general practice are self-employed and controlled by their practice agreements
• (in the UK) a senior civil servant in charge of a particular section.

• 2 [in singular] a sum of money lent or invested, on which interest is paid:the winners are paid from the interest without even touching the principal

• 3a person for whom another acts as an agent or representative:stockbrokers in Tokyo act as agents rather than as principals

• 4 Law the person directly responsible for a crime.
• historical each of the combatants in a duel.

• 5a main rafter supporting purlins.

• 6an organ stop sounding a main register of open flue pipes typically an octave above the diapason: all the principals are on one manual