principle

 
Pronunciation: /ˈprɪnsɪp(ə)l/

noun

  • 1a fundamental truth or proposition that serves as the foundation for a system of belief or behaviour or for a chain of reasoning: the basic principles of justice
  • (usually principles) a rule or belief governing one’s behaviour: struggling to be true to their own principles [mass noun]: she resigned over a matter of principle
  • [mass noun] morally correct behaviour and attitudes: a man of principle
  • 2a general scientific theorem or law that has numerous special applications across a wide field.
  • a natural law forming the basis for the construction or working of a machine: these machines all operate on the same general principle
  • 3a fundamental source or basis of something: the first principle of all things was water
  • a fundamental quality determining the nature of something: the combination of male and female principles
  • [with adjective] Chemistry an active or characteristic constituent of a substance, obtained by simple analysis or separation: the active principle of Spanish fly

Phrases

in principle

as a general idea or plan, although the details are not yet established: the government agreed in principle to a peace plan that included a ceasefire
used to indicate that although something is theoretically possible, in reality it may not actually happen: in principle, the banks are entitled to withdraw these loans when necessary

on principle

because of or in order to demonstrate one’s adherence to a particular belief: he refused, on principle, to pay the fine

Origin:

late Middle English: from Old French, from Latin principium 'source', principia (plural) 'foundations', from princeps, princip- 'first, chief'

The words principle and principal are pronounced in the same way but they do not have the same meaning. Principle is normally used as a noun meaning ‘a fundamental basis of a system of thought or belief’, as in this is one of the basic principles of democracy. Principal, on the other hand, is normally an adjective meaning ‘main or most important’, as in one of the country’s principal cities. Principal can also be a noun, where it is used to refer to the most senior or most important person in an organization or other group: the deputy principal.