 Principle and Principle from espressoenglish.net Principle, ending in P-L-E, is a noun, meaning a fundamental idea, belief, philosophy, or rule. For example, my daughter is learning the basic principles of physics in her science class. Power in the hands of the people is one of the key principles of democracy. He would never steal from the company. He is a man of high principles. High principles means good and strong moral beliefs. The word principle, ending in P-A-L, can be an adjective, meaning main or most important. For example, the lake is the principle water source for the city. It's the main water source. The city gets most of its water from the lake. Principle, ending in P-A-L, can also be a noun, referring to a person, who is the director of an elementary, middle, or high school. For example, students who misbehave are sent to the principal's office. Principle, as a noun, has another meaning in finance. It means the original amount of a debt, not counting the interest, the extra money that accumulates over time as the debt is not paid. For example, at a 10% interest rate, a principle of $1,000 will accumulate $100 of interest. This was a free sample lesson from the new e-book, 600-plus Confusing English Words Explained, available at espressoenglish.net. In this book, you'll learn words that both English learners and native English speakers confuse.