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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

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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

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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

"We are not opposed to renewable energy in principle," said Lesley Jesurajan, a leading figure in the local civil society group OPEnE.

From Barron's ● Oct. 25, 2026

More broadly, the findings highlight an important principle of animal evolution: physical structure does not necessarily determine the full range of movements an animal can perform.

From Science Daily ● Oct. 24, 2026

Neglecting his own first principle, Mr. Firestein quotes authors without questioning their authority or offering rival views.

From The Wall Street Journal ● Oct. 23, 2026

"It is an important proof of principle for the field, although we shouldn't get ahead of the evidence," he said.

From BBC ● Oct. 23, 2026

This principle of ever-more-exact measurement derives from Tycho Brahe; in tightening up the relationship between evidence and theory in physics, Galileo was extrapolating from the practices of the astronomers.

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

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

Ferociously cool, Control became an MTV staple thanks to eye-catching videos like Nasty and The Pleasure Principle – all featuring Janet's punchy choreography.

From BBC ● Jul. 24, 2024

To all the stubborn parties obstinately concerned with this matter, it was The Principle of the Thing.

From "The Milagro Beanfield War" by John Nichols

To overcome these limitations, the researchers revisited the foundational principles of transformation thermotics, a field that explores how heat can be redirected through specially designed materials.

From Science Daily ● Oct. 26, 2026

There would be no need to manufacture mirror organisms simply to explore whether the underlying detection principles work.

From Science Daily ● Oct. 24, 2026

I’ve written previously about low-pressure potluck entertaining, and the same principles work beautifully here.

From Salon ● Oct. 20, 2026

I called the Portuguese manager to explore his influences, principles and the ever-changing tactical landscape.

From BBC ● Oct. 17, 2026

But a man has to have his principles.

From "The Interrupted Tale" by Maryrose Wood

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