The DICT Development Group

  Infallible \In*fal"li*ble\, a. [Pref. in- not + fallible: cf. F.
     infallible.]
     [1913 Webster]
     1. Not fallible; not capable of erring; entirely exempt from
        liability to mistake; unerring; inerrable. --Dryden.
        [1913 Webster]
  
     2. Not liable to fail, deceive, or disappoint; indubitable;
        sure; certain; as, infallible evidence; infallible
        success; an infallible remedy.
        [1913 Webster]
  
              To whom also he showed himself alive, after his
              passion, by many infallible proofs.   --Acts i. 3.
        [1913 Webster]
  
     3. (R. C. Ch.) Incapable of error in defining doctrines
        touching faith or morals. See Papal infallibility, under
        Infallibility.
        [1913 Webster]

  infallible
      adj 1: incapable of failure or error; "an infallible antidote";
             "an infallible memory"; "the Catholic Church considers
             the Pope infallible"; "no doctor is infallible" [ant:
             fallible]

  79 Moby Thesaurus words for "infallible":
     absolute, acceptable, agreeable, beyond all praise, certain,
     chaste, close, constant, correct, defectless, delicate, dependable,
     direct, effective, efficacious, efficient, even, exact, express,
     faithful, faultless, fine, flawless, foolproof, handy, helpful,
     ideal, immaculate, impeccable, indefectible, indefective,
     inerrable, inerrant, irreproachable, just right, mathematical,
     micrometrically precise, microscopic, nice, oracular, peerless,
     perfect, pinpoint, precise, pure, refined, reliable, religious,
     religiously exact, rigid, rigorous, satisfactory, satisfying,
     scientific, scientifically exact, secure, severe, sinless,
     spotless, square, stainless, strict, subtle, sure, surefire,
     taintless, unadulterated, unblemished, uncontaminated,
     undeceivable, undeviating, unerring, unfailing, unfaultable,
     unmistaken, unmixed, unspotted, untainted, useful