principal / principle

A principle (n.) is a fundamental idea, belief, philosophy, or rule:

  • 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’s a man of high principles.

    The word principal has three meanings:

    1. As an adjective: the main or most important The lake is the principal water source for the city.

    2. As a noun: the director of an elementary, middle, or high school Students who misbehave are sent to the principal’s office.

    3. As a noun (finance): the original amount of a debt (not counting the interest

    – the extra money that accumulates over time as the debt is not paid):

    At a 10% interest rate, a principal of $1,000 will accumulate $100 of interest.