axiom

Concise Oxford English Dictionary © 2008 Oxford University Press:
axiom /ˈaksɪəm/

▶noun

• 1 an accepted statement or proposition regarded as being self-evidently true.

• 2 chiefly Mathematics a statement or proposition on which an abstractly defined structure is based.

– derivatives
axiomatic adjective,
axiomatically adverb.

– origin C15: from Fr. axiome or L. axioma, from Gk axiōma, from axios ‘worthy’.