1. The head or director of a school or of a college in England: Mr. Straight wa the principal at the elementary school that Virginia attended.
2. A person who takes a leading part in any activity, as a play; a chief actor or performer: Since Mary was the principal in the play at school, she had to take part in all of the rehearsals each afternoon.
3. The first player of a division of instruments in an orchestra (except the concertmaster): The principals of each string section in a chamber orchestra always sits in the first row of players.
4. Something of primary or chief importance: The principal or main reason for going to Toronto was to visit her daughter and sister.

Learn how to distinguish between principal and principle.

1. First or highest in ranks, importance, values, etc.; chiefs.
2. Of the natures of, or constituting principals; such as, significant principals were invested in the company.