- Def: Infallible 1. absolutely trustworthy or sure; 2. unfailing in effectiveness or operation; certain; 3. not fallible; exempt from liability to error, as persons, their judgment, or pronouncements; 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; 5. Incapable of error; failing; certain;
- Origin: 1375–1425; late ME < ML infallibilis. See in-3, fallible;
- Synonyms: acceptable, accurate, agreeable, apodictic, authoritative, certain, correct, effective, effectual, efficacious, efficient, exact, faultless, flawless, foolproof, handy, helpful, impeccable, incontrovertible, inerrable, inerrant, omniscient, perfect, positive, reliable, satisfactory, satisfying, sure, surefire, true, trustworthy, unbeatable, undeceivable, unerring, unfailing, unimpeachable, unquestionable, useful.