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.