■ noun
1》 a fundamental truth or proposition serving as the foundation for belief or action.
↘a rule or belief governing one's personal behaviour.
↘morally correct behaviour and attitudes: a man of ~.
2》 a general scientific theorem or natural law.
3》 a fundamental source or basis of something.
↘a fundamental quality or attribute.
4》 Chemistry an active or characteristic constituent of a substance.
Phrases
in ~ in theory.
on ~ because of one's adherence to a particular belief.
Origin
ME: from OFr., from L. principium 'source', principia (plural) 'foundations', from princeps , princip- 'first, chief'.
Usage
Note that ~ and principal 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 ~s 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 . As a noun principal refers to the most senior or most important person in an organization: the deputy principal .