adjective (a)

• incapable of failure or error(adj.all)

  Example:
  An infallible antidote.
  An infallible memory.
  The Catholic Church considers the Pope infallible.
  No doctor is infallible.
  

  Antonym:
  fallible
  

  source: wordnet30
• Not fallible; not capable of erring; entirely exempt from liability to mistake; unerring; inerrable.(adjective)

  source: webster1913