principle

noun

prin·​ci·​ple ˈprin(t)-s(ə-)pəl 

-sə-bəl

1

a

: a comprehensive and fundamental law, doctrine, or assumption

well-established economic principles

b(1)

: a rule or code of conduct

Plagiarism is against the school's principles.

… a new series of laws declared a fourth principle: the colonies could not make or export items that competed with English products …

—Mary Beth Norton et al.

(2)

: habitual devotion to what is right

a leader of principle

As a matter of principle, he would not accept the gift.

The photographer refused on principle to sell photos to the tabloids.

c

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

the principle of the internal-combustion engine

Note: Do not confuse this word, principle, with the similar principal. As a noun, principal has various meanings referring to someone with controlling authority ("the school principal") or in a leading position ("the ballet's two principals"), as well as meanings relating to finance, law, and architecture. As an adjective, principal typically means "most important" ("the principal reason").

2

: a primary source : origin

The principle of his great success lay in the fact of his appearance at a critical epoch.

—The North American Review

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

the active principle of this drug

4

Principle Christian Science : a divine principle : god

see also in principle

Synonyms of principle

• 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

The principle is simple, yet beautiful. —John Metcalfe, Mercury News, 24 Dec. 2025

Taken together, these reforms reflect a simple principle. —Jay Obernolte, Oc Register, 24 Dec. 2025

In November, the parties originally agreed to a deal in principle, which ended weeks of rotating strikes. —Glenn Taylor, Sourcing Journal, 23 Dec. 2025

This ancient Chinese art isn't just for arranging your space—its principles can also be applied to picking paint colors. —Maria Sabella, Better Homes & Gardens, 23 Dec. 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