principal

noun1 of 2

1. most important; main; 2. the person in charge of a (US) public school

• “This is one of the principal arguments against your plan.”Tatoeba
• “He even suspected that the man was the principal offender.”Tatoeba

Sentences from Tatoeba show real usage. A word can have several meanings, so a sentence may use another one.

adjective2 of 2

Primary; most important; first level in importance.