Longman Dictionary of Contemporary English homepage

Date: 1300-1400
Language: French
Origin: principe, from Latin principium 'beginning', from princeps; PRINCE

principle

noun
     
prin‧ci‧ple S3 W1
1

moral rule

[uncountable and countable] a moral rule or belief about what is right and wrong, that influences how you behave:
Schools try to teach children a set of principles.
He prided himself on his high moral principles (=strong ideas about how it is right or wrong to behave)
He's got no principles at all!
He refused to give me any more money as a matter of principle.
against somebody's principles
It's against my principles to accept gifts from clients.
man/woman of principle (=a man or woman with strong moral ideas)
He considered himself to be a man of principle.
2

idea behind something

[countable] the basic idea that a plan or system is based on:
The general principle is that education should be available to all children up to the age of 16.
basic/fundamental/guiding principle
the basic principles of business management
principle of
the principles of French law
principle that
Reflexology is based on the principle that specific areas on the feet correspond to different parts of the body.
on a principle
The project worked on the principle that each person's experience was equally valuable.
principle behind
the principles behind government policies
He called for a return to first principles (=the most important ideas) of road safety for children.
Similar principles apply in the case of older children (=the principles are the same as others that have been mentioned).
3

in principle

a) if something is possible in principle, there is no good reason why it should not happen, but it has not actually happened yet:
In principle, the new software should make the accounting system a lot simpler.
b) if you agree to something in principle, you agree about a general plan or idea but have not yet considered the details:
They have accepted the idea in principle.
The government has agreed in principle to a referendum.
4

rules of a process

[countable] a rule which explains the way something such as a machine works, or which explains a natural force in the universe:
Archimedes' principle
principle of
the basic principles of physics
! Do not confuse the noun principle (=a basic rule) with the noun and adjective principal, which have the same pronunciation but different meanings.

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