Definition: Axiom

An axiom is a statement that identifies the base of knowledge and of any further statement pertaining to that knowledge, a statement necessarily contained in all others, whether any particular speaker chooses to identify it or not. An axiom is a proposition that defeats its opponents by the fact that they have to accept it and use it in the process of any attempt to deny it.

Source:  John Galt (Fictional Character)
Taken From:  Ayn Rand's Atlas Shrugged (1957)