A Principle

Lingual Usages

A fundamental assumption or guiding belief.
A rule used to choose among solutions to a problem.
(sometimes pluralized) Moral rule or aspect.
(physics) A rule or law of nature, or the basic idea on how the laws of nature are applied. q
A fundamental essence, particularly one producing a given quality. .
(obsolete) A beginning.
A source, or origin; that from which anything proceeds; fundamental substance or energy; primordial substance; ultimate element, or cause.
An original faculty or endowment.

Principle ("moral rule"), as a noun, is often confused with principal, which can be an adjective ("most important") or a noun ("school principal"). A memory aid to avoid this confusion is: "The principal alphabetic principle places A before E".