Infallible

Not fallible; not capable of erring; entirely exempt from liability to mistake; unerring; inerrable.

Not liable to fail, deceive, or disappoint; indubitable; sure; certain; as, infallible evidence; infallible success; an infallible remedy.

Incapable of error in defining doctrines touching faith or morals. See Papal infallibility, under Infallibility.