infallible

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 ]