Principle/ˈprɪnsəpl/ Definition 1 of 5Pro Tip 1/2Universal Application Think of 'principle' as a core rule or idea that applies broadly, not just to one specific case. The principle of equal rights shapes laws worldwide. Pro Tip 2/2Foundational Concept 'Principle' often refers to an idea that forms the basis for other concepts or actions. Free speech is a fundamental principle of a free society.