1. A chief or head.
2. The head or director of a school or; especially, in England, a college.
3. A person who takes a leading part in any activity, as a play; a chief actor or performer.
4. The first player of a division of instruments in an orchestra (except the leader of the first violins).
5. Something of primary or chief importance.

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.