a self-evident truth that requires no proof.

a universally accepted principle or rule.

Logic, Mathematics . a proposition that is assumed without proof for the sake of studying the consequences that follow from it.

noun

absurdity , ambiguity , foolishness , nonsense , paradox

noun

adage , aphorism , apothegm , device , dictum , fundamental , law , maxim , moral , postulate , precept , proposition , proverb , saying , theorem , truism , truth , principle , universal , byword , canon , convention , motto , rule , saw , sentence , standard , witticism