1. He would never accept a bribe. He’s got very strong principles.
2. The person in charge of a school in the UK is the headmaster or headmistress, but in the US he or she is called the principal.
3. The Opera House is one of the principal tourist attractions in Sydney.
4. I would never do that in a million years. I’m a man of principle, just like you.

principal = principal, director (de un colegio)
principle = principios, moral