The Collaborative International Dictionary of English v.0.48:

Axiomatic \Ax`i*o*mat"ic\, Axiomatical \Ax`i*o*mat"ic*al\, a.
   [Gr. ?.]
   Of or pertaining to an axiom; having the nature of an axiom;
   self-evident; characterized by axioms. "Axiomatical truth."
   --Johnson.
   [1913 Webster]

         The stores of axiomatic wisdom.          --I. Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

axiomatic
    adj 1: evident without proof or argument; "an axiomatic truth";
           "we hold these truths to be self-evident" [syn:
           axiomatic, self-evident, taken for granted(p)]
    2: containing aphorisms or maxims; "axiomatic wisdom" [syn:
       axiomatic, aphoristic]
    3: of or relating to or derived from axioms; "axiomatic
       physics"; "the postulational method was applied to geometry"-
       S.S.Stevens [syn: axiomatic, axiomatical,
       postulational]

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "axiomatic":
   absolute, actual, admitting no question, aphoristic, apparent,
   clear, clear as crystal, confirmable, crisp, crystal-clear,
   demonstrable, demonstratable, discernible, distinct, epigrammatic,
   evident, explicit, express, factual, formulaic, formulistic,
   gnomic, historical, inappealable, incontestable, incontrovertible,
   indisputable, indubitable, irrefragable, irrefutable, manifest,
   noticeable, observable, obvious, open-and-shut, palpable, patent,
   perceivable, perceptible, perspicuous, pithy, plain, plain as day,
   platitudinous, pointed, provable, proverbial, pungent, real,
   seeable, self-evident, self-explaining, self-explanatory,
   sententious, succinct, tangible, terse, testable, to be seen,
   unanswerable, unconfutable, undeniable, unimpeachable,
   unmistakable, unquestionable, unrefutable, verifiable, visible