The Collaborative International Dictionary of English v.0.48:

Reliable \Re*li"a*ble\ (r?-l?"?-b'l), a.
   Suitable or fit to be relied on; worthy of dependance or
   reliance; trustworthy. "A reliable witness to the truth of
   the miracles." --A. Norton.
   [1913 Webster]

         The best means, and most reliable pledge, of a higher
         object.                                  --Coleridge.
   [1913 Webster]

         According to General Livingston's humorous account, his
         own village of Elizabethtown was not much more
         reliable, being peopled in those agitated times by
         "unknown, unrecommended strangers, guilty-looking
         Tories, and very knavish Whigs."         --W. Irving.
   [1913 Webster]

   Note: Some authors take exception to this word, maintaining
         that it is unnecessary, and irregular in formation. It
         is, however, sanctioned by the practice of many careful
         writers as a most convenient substitute for the phrase
         to be relied upon, and a useful synonym for
         trustworthy, which is by preference applied to persons,
         as reliable is to things, such as an account,
         statement, or the like. The objection that adjectives
         derived from neuter verbs do not admit of a passive
         sense is met by the citation of laughable, worthy of
         being laughed at, from the neuter verb to laugh;
         available, fit or able to be availed of, from the
         neuter verb to avail; dispensable, capable of being
         dispensed with, from the neuter verb to dispense. Other
         examples might be added.
         [1913 Webster] -- Re*li"a*ble*ness, n. --
         Re*li"a*bly, adv.
         [1913 Webster]

WordNet (r) 3.0 (2006):

reliable
    adj 1: worthy of reliance or trust; "a reliable source of
           information"; "a dependable worker" [syn: reliable,
           dependable] [ant: undependable, unreliable]
    2: worthy of being depended on; "a dependable worker"; "an
       honest working stiff"; "a reliable sourcSFLe of information";
       "he was true to his word"; "I would be true for there are
       those who trust me" [syn: dependable, honest, reliable,
       true(p)]
    3: conforming to fact and therefore worthy of belief; "an
       authentic account by an eyewitness"; "reliable information"
       [syn: authentic, reliable]

Moby Thesaurus II by Grady Ward, 1.0:

138 Moby Thesaurus words for "reliable":
   absolute, accurate, adducible, admissible, apposite, attestative,
   attested, attestive, authentic, authenticated, balanced, based on,
   believable, calculable, certain, circumstantial, circumstantiated,
   cogent, colorable, compelling, conceivable, conclusive, confirmed,
   conscientious, convincing, cool, credible, cumulative, damning,
   decisive, dependable, determinative, documentary, documented,
   evidential, evidentiary, ex parte, eye-witness, factual, fail-safe,
   faithful, faithworthy, fast, fiducial, fiduciary, final, firm,
   firm as Gibraltar, firsthand, founded on, grounded on, guaranteed,
   harmless, hearsay, honest, honorable, imperturbable, implicit,
   in equilibrium, incontrovertible, incorruptible, indicative,
   indisputable, inerrable, inerrant, infallible, invincible,
   inviolable, invulnerable, irrefutable, irresistible, material,
   meaningful, nuncupative, overwhelming, plausible, predictable,
   presumptive, principled, probative, proven, punctilious, reputable,
   responsible, riskless, safe, secure, significant, solid, sound,
   stable, staunch, steadfast, steady, straight, substantial,
   suggestive, sure, surefire, symptomatic, telling, tenable, tested,
   to be trusted, tried, tried and true, true, trustable, trusted,
   trustworthy, trusty, undangerous, unerring, unexceptionable,
   unfailing, unfalse, unflappable, unflinching, unhazardous,
   unimpeachable, unperfidious, unperilous, unprecarious,
   unquestionable, unrisky, unshakable, untreacherous, unwavering,
   valid, validated, verified, warranteed, weighty, well-balanced,
   well-founded, well-grounded, without nerves, worthy of faith