axiom

noun
  1. A statement or proposition that is regarded as being established, accepted, or self-evidently true, often serving as a starting point for further reasoning or arguments. noun
    In mathematics, an axiom is a basic assumption about a system that does not require proof.
    The axiom that 'all men are created equal' is fundamental to democratic societies.
  2. A universally accepted principle or rule that is not necessarily self-evident but is accepted as true for the sake of argument or investigation. noun
    The axiom 'the customer is always right' is often used in the service industry.
    In business, the axiom that 'time is money' drives many decisions.