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• principle
  principle

  noun

  an accepted or professed rule of action or conduct.
• Principle
  Principle

  noun

  Christian Science another word for God

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principle

American  

[prin-suh-puhl] / ˈprɪn sə pəl /

noun

• principles
  plural

1. an accepted or professed rule of action or conduct.

   a person of good moral principles.

2. a fundamental, primary, or general law or truth from which others are derived.

   the principles of modern physics.

   Synonyms:

   proposition, postulate, axiom, theorem

3. a fundamental doctrine or tenet; a distinctive ruling opinion.

   the principles of the Stoics.

4. principles, a personal or specific basis of conduct or management.

   to adhere to one's principles; a kindergarten run on modern principles.

5. guiding sense of the requirements and obligations of right conduct.

   a person of principle.

   Synonyms:

   honor, rectitude, probity, integrity

6. an adopted rule or method for application in action.

   a working principle for general use.

7. a rule or law exemplified in natural phenomena, the construction or operation of a machine, the working of a system, or the like.

   the principle of capillary attraction.

8. the method of formation, operation, or procedure exhibited in a given case.

   a community organized on the patriarchal principle.

9. a determining characteristic of something; essential quality.

10. an originating or actuating agency or force.

    growth is the principle of life.

11. an actuating agency in the mind or character, as an instinct, faculty, or natural tendency.

    the principles of human behavior.

12. Chemistry. a constituent of a substance, especially one giving to it some distinctive quality or effect.

13. Obsolete. beginning or commencement.

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idioms

1. in principle, in essence or substance; fundamentally.

   to accept a plan in principle.

2. on principle,

   1. according to personal rules for right conduct; as a matter of moral principle.

      He refused on principle to agree to the terms of the treaty.

   2. according to a fixed rule, method, or practice.

      He drank hot milk every night on principle.

principle ¹ British  

/ ˈprɪnsɪpəl /

noun

1. a standard or rule of personal conduct

   a man of principle

2. (often plural) a set of such moral rules

   he'd stoop to anything

   he has no principles

3. adherence to such a moral code; morality

   it's not the money but the principle of the thing

   torn between principle and expediency

4. a fundamental or general truth or law

   first principles

5. the essence of something

   the male principle

6. a source or fundamental cause; origin

   principle of life

7. a rule or law concerning a natural phenomenon or the behaviour of a system

   the principle of the conservation of mass

8. an underlying or guiding theory or belief

   the hereditary principle

   socialist principles

9. chem a constituent of a substance that gives the substance its characteristics and behaviour

   bitter principle

10. in theory or essence

11. because of or in demonstration of a principle

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Principle ² British  

/ ˈprɪnsɪpəl /

noun

1. Christian Science another word for God

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principle More Idioms  

1. see in principle; on principle.

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Usage

Principle and principal are often confused: the principal (not principle ) reason for his departure; the plan was approved in principle (not in principal )

Commonly Confused

See principal.

Synonym Usage

Principle, canon, rule imply something established as a standard or test, for measuring, regulating, or guiding conduct or practice. A principle is a general and fundamental truth that may be used in deciding conduct or choice: to adhere to principle. Canon, originally referring to an edict of the Church (a meaning that it still retains), is used of any principle, law, or critical standard that is officially approved, particularly in aesthetics and scholarship: canons of literary criticism. A rule, usually something adopted or enacted, is often the specific application of a principle: the golden rule.

Other Word Forms

Noun Inflected Forms

• principles
  plural

Etymology

Origin of principle

First recorded in 1350–1400; Middle English, alteration of Middle French principe or Latin prīncipium, on the analogy of manciple; see principium

Explanation

A principle is a kind of rule, belief, or idea that guides you. You can also say a good, ethical person has a lot of principles. In general, a principle is some kind of basic truth that helps you with your life. "Be fair" is a principle that guides (or should guide) most people and businesses. A politician who tries to do the right thing rather than win votes is acting on principle. A person who has principles is a good, decent person. On the other hand, if you say someone has no principles, that means they're dishonest, corrupt, or evil.

Example Sentences

See Examples For:

principle Principle principles

The same conservation principle also applies on the scale of the universe.

From Science Daily ● Aug. 16, 2026

“It’s a kind of principle that lots of people can claim, and do claim — and they claim it for their own purposes,” Wenger said in an interview.

From Salon ● Aug. 14, 2026

In 2018, for example, the company undertook a major reorganization of senior management based on the principle of division of labor by comparative advantage.

From The Wall Street Journal ● Aug. 12, 2026

The Reds agreed a deal in principle in January, but the £2.6m transfer became official this summer, once Ndukwe turned 18.

From BBC ● Aug. 11, 2026

This principle was employed by della Porta in 1606, and in 1625 Salomon de Caus devised a steam fountain.

From "The Invention of Science" by David Wootton

Ehrlich was often labeled a neo-Malthusian, a reference to the 18th-century British political economist Thomas Malthus, best known for “An Essay on the Principle of Population.”

From The Wall Street Journal ● Mar. 17, 2026

The Premack Principle is a motivational behavioral technique based on a reward system.

From Los Angeles Times ● Jan. 20, 2025

“They have to have fundraisers to get a car fixed. Jamie Principle never made a dollar from any of his records.”

From BBC ● Oct. 16, 2024

Thus a key Principle of our rule of law is that we must "respect, support, and defend the constitutional rights of all Americans" with fairness and due process of law.

From Salon ● Sep. 3, 2024

Second is the Principle of Consanguinity, which says, ‘a piece of a thing can represent the whole of a thing.’

From "The Name of the Wind" by Patrick Rothfuss

Many of the diet’s principles are surprisingly simple, which could explain its enduring popularity and effectiveness and why nutrition experts often describe it as an eating pattern rather than a diet.

From MarketWatch ● Aug. 16, 2026

Kinder rejects criticism that aid agencies have had to compromise on principles to keep their projects in place.

From BBC ● Aug. 14, 2026

Scientists are getting a clearer picture of how thermodynamics behaves in the quantum world, and that progress could benefit both quantum technology and our understanding of familiar thermodynamic principles.

From Science Daily ● Aug. 14, 2026

While Guardiola had principles he stuck to throughout his career, he did not stick to one system.

From BBC ● Aug. 14, 2026

These fairs often contained “Mendel booths,” where the principles of genetics and the laws of inheritance were demonstrated using puppets.

From "The Gene" by Siddhartha Mukherjee

Related Words

• assumption
• basis
• convention
• doctrine
• ethic
• foundation
• fundamental
• precept
• proposition
• regulation
• rule
• truth