Principle v. principal

Principle and principal are pronounced the same, but they are different words. To begin with principle is a noun only and principal is both an adjective and a noun.

Principle means tenet, ethos, moral position or stance, fundamental belief, rule, precept, dictum, dogma.

Principal, as an adjective, means first, main, key, dominant, major, primary, chief. 

Principal, as a noun, means “the one who is first (i.e. boss)”, and is used to indicate the head of a school or  the main party in a financial transaction. It also refers to the main sum of money borrowed  or lent (the cost of servicing the debt is called interest).

Just remember that principal, meaning “first”, is the one with the letter A, the first letter of the alphabet.