principle

noun

prin·​ci·​ple ˈprin(t)-s(ə-)pəl 

-sə-bəl

1

a

: a comprehensive and fundamental law, doctrine, or assumption

b(1)

: a rule or code of conduct

(2)

: habitual devotion to right principles

a man of principle

c

: the laws or facts of nature underlying the working of an artificial device

2

: a primary source : origin

3

a

: an underlying faculty or endowment

such principles of human nature as greed and curiosity

b

: an ingredient (such as a chemical) that exhibits or imparts a characteristic quality

4

capitalized Christian Science : a divine principle : god

Principle vs. Principal: Usage Guide

Evidence of confusion between principle and principal can be found even in publications overseen by professional editors. To keep these words straight, remember that principle functions only as a noun, and in its most common uses refers to a basic rule or law, as in

a guiding principle

or

a matter of principle.

If you are looking for an adjective form of this word, you must use principled, as in

taking a principled stand.

Principal functions as both a noun and an adjective. The noun has various meanings referring to someone with controlling authority

the school principal

or in a leading position

the ballet's two principals

, but also has meanings relating to finance, law, and architecture. As an adjective, principal typically means "most important," as in

the principal reason.

Phrases

in principle

: with respect to fundamentals

prepared to accept the proposition in principle

Synonyms

• elements
• grammar
• basis
• philosophy

Examples of principle in a Sentence

Urban guerrilla warfare was futile against a thermonuclear superstate that would stop at nothing to defend the profit principle. —Philip Roth, American Pastoral, 1997

Better, of course, to take a higher road, operate on the principle of service and see if things don't turn out better … —Richard Ford, Independence Day, 1995

Pointlessness was life's principle, and it spread its sadness. —Arthur Miller, Timebends, 1987

His investment strategy is based on the principle that the stock market offers the best returns for long-term investors.

the basic principles of hydraulics

Recent Examples on the Web

Your values, your long-term goals and your decision principles. —Benjamin Laker, Forbes.com, 27 June 2025

The conservative Supreme Court on Friday delayed ruling on President Trump’s effort to end birthright citizenship, the bedrock principle that anyone born in the U.S. is automatically a citizen. —Dave Goldiner, New York Daily News, 27 June 2025

At a time when establishing clarity of first principles has never been more urgent, UF’s law school practically dared anyone to criticize the award for whitewashing the Constitution. —Orlando Sentinel, The Orlando Sentinel, 27 June 2025

Finally, while its decision in CASA dealt only with the injunctive powers of courts, the Court should act on its own principles and return as swiftly as possible to resolve Trump’s challenge to constitutional birthright citizenship. —The Editors, National Review, 27 June 2025

Word History

Etymology

Middle English, from Middle French principe, principle, from Old French, from Latin principium beginning, from princip-, princeps initiator — more at prince

First Known Use

14th century, in the meaning defined at sense 2

Phrases Containing principle

• acceleration principle
• a matter of principle
• anthropic principle
• as a matter of principle
• Bernoulli's principle
• exclusion principle
• Hardy-Weinberg principle
• Heisenberg uncertainty principle
• indeterminacy principle
• on principle
• Pauli exclusion principle
• pleasure principle
• strong anthropic principle
• uncertainty principle
• weak anthropic principle

Rhymes for principle

• principal

Kids Definition

principle

noun

prin·​ci·​ple ˈprin(t)-s(ə-)pəl 

-sə-bəl

1

: a general or basic truth on which other truths or theories can be based

scientific principles

2

: a rule of conduct

a person of high principles

3

: a law or fact of nature which makes possible the working of a machine or device

the principle of magnetism

the principle of the lever

Medical Definition

principle

noun

prin·​ci·​ple ˈprin(t)-sə-pəl 

1

: a comprehensive and fundamental law, doctrine, or assumption

2

: an ingredient (as a chemical) that exhibits or imparts a characteristic quality

the active principle of a drug