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