axiom

axiom is a Noun

Definition:

[1] A self-evident and necessary truth, or a proposition whose truth is so evident as first sight that no reasoning or demonstration can make it plainer; a proposition which it is necessary to take for granted; as, "The whole is greater than a part;" "A thing can not, at the same time, be and not be."

[2] An established principle in some art or science, which, though not a necessary truth, is universally received; as, the axioms of political economy.