Infallible

1. a. Incapable of error in defining doctrines touching faith or morals. See Papal infallibility, under Infallibility.
2. a. Not fallible; not capable of erring; entirely exempt from liability to mistake; unerring; inerrable.
3. a. Not liable to fail, deceive, or disappoint; indubitable; sure; certain; as, infallible evidence; infallible success; an infallible remedy.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.