Principal and principle are homophones. I’ve come across principal misused more often than principle, but it’s common to get them both confused. Principle is usually a noun but principal can be an adjective or a noun.
- first in order of importance or value
- the most important or senior person in an organisation
- a fundamental truth, proposition, rule or law
- a moral rule or set of such morals
- a general scientific theorem or law
- a fundamental source or basis of something
My tip: principal is spelled with an a, which is the first letter in the alphabet – and a principle is often a rule.