"Principal": Chefe de um escritório de advocacia ou engenharia ou diretor de uma escola.
Principal (noun; adjective): "chief," e.g. the principal role in a play is the chief (main) role while the principal in a school or law or architecture firm is the chief of the firm, the highest member of its hierarchy.
Principle (noun) ['prin-sê-pêl]: A fundamental truth or rule, especially a rule of moral character, as a woman of principle.
Fonte: Dr. Language, YourDictionary.com