The Collaborative International Dictionary of English v.0.48:

Provable \Prov"a*ble\, a. [See Prove, and cf. Probable.]
   Capable of being proved; demonstrable. -- Prov"a*ble*ness,
   n. -- Prov"a*bly, adv.
   [1913 Webster] Provand

WordNet (r) 3.0 (2006):

provable
    adj 1: capable of being demonstrated or proved; "obvious lies";
           "a demonstrable lack of concern for the general welfare";
           "practical truth provable to all men"- Walter Bagehot
           [syn: demonstrable, provable]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "provable":
   absolute, actual, admitting no question, apodictic, attestable,
   authenticatable, checkable, confirmable, demonstrable,
   demonstratable, evincible, factual, historical, inappealable,
   incontestable, incontrovertible, indisputable, indubitable,
   irrefragable, irrefutable, real, self-evident, substantiatable,
   supportable, sustainable, testable, unanswerable, unconfutable,
   undeniable, unimpeachable, unquestionable, unrefutable,
   validatable, verifiable