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late 15c., from Middle French axiome, from Latin axioma, from Greek axioma "authority," literally "that which is thought worthy or fit," from axioun "to think worthy," from axios "worthy, worth, of like value, weighing as much," from PIE adjective *ag-ty-o- "weighty," from root *ag- "to drive, draw, move" (see act (n.)).
Axioms in philosophy are not axioms until they are proved upon our pulses. [Keats, letter, May 3, 1818]
In mathematics, a statement that is unproved but accepted as a basis for other statements, usually because it seems so obvious.
Note: The term axiomatic is used generally to refer to a statement so obvious that it needs no proof.