in·fal·li·ble /ɪnˈfæləbəl/ [in-fal-uh-buhl]
–adjective 1. absolutely trustworthy or sure: an infallible rule.
2. unfailing in effectiveness or operation; certain: an infallible remedy.
3. not fallible; exempt from liability to error, as persons, their judgment, or pronouncements: an infallible principle.
4. Roman Catholic Church. immune from fallacy or liability to error in expounding matters of faith or morals by virtue of the promise made by Christ to the Church.
–noun 5. an infallible person or thing.