adjective 1. first or highest in rank, importance, value, etc.; chief; foremost.
2. of the nature of principal, or a capital sum.
–noun 3. a chief, head, or governing officer.
4. the head teacher of a school, college, etc.
5. someone who takes a leading part; a chief actor or doer.
6. the first player of a division of instruments in an orchestra (excepting the leader of the first violins).
7. something of principal or chief importance.
a. a person authorising another (an agent) to represent him or her.
b. a person directly responsible for a crime, either as actual perpetrator or as abetter present at its commission. Compare accessory (def. 3).
9. a person primarily liable for an obligation (opposed to an endorser).
10. the main body of an estate, etc., as distinguished from income.
11. Commerce a capital sum, as distinguished from interest or profit.
a. an organ stop otherwise called diapason.
b. the subject of a fugue (opposed to answer).
13. the central structure of a roof which determines its shape and supports it.
14. each of the combatants in a duel, as distinguished from the seconds.[Middle English, from Latin principālis first, chief]
Usage: Principal is commonly confused with principle.