plural principles
1
: a moral rule or belief that helps you know what is right and wrong and that influences your actions
He has good principles.
It's against my principles to cheat. [=I believe that cheating is wrong]
As a matter of principle, he would not accept the gift. [=he did not feel that it was right to accept the gift]
She refused on principle [=because of her beliefs] to give toy guns to the children.
2
: a basic truth or theory : an idea that forms the basis of something
well-established economic principles
His investment strategy is based on the principle that the stock market offers the best returns for long-term investors.
3
: a law or fact of nature that explains how something works or why something happens
the basic principles of hydraulics/magnetism
Cite this Entry
“Principle.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/principle. Accessed 22 Jul. 2026.
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