noun A fundamental assumption, fundamental law or guiding belief.
We need some sort of principles to reason from.
noun A rule used to choose among solutions to a problem.
The principle of least privilege holds that a process should only receive the permissions it needs.
noun Moral rule or aspect.
I don't doubt your principles.
noun A rule or law of nature, or the basic idea on how the laws of nature are applied.
Bernoulli's principle
noun A fundamental essence, particularly one producing a given quality.
Many believe that life is the result of some vital principle.
noun A chemical compound within plant or animal tissue that is characteristic of it and more or less peculiar to it, such that it defines the character of that tissue from a human viewpoint (as for example nicotine in tobacco).
the active principle
noun A source, or origin; that from which anything proceeds; fundamental substance or energy; primordial substance; ultimate element, or cause.