infallible

UK: /ɪnˈfælɪb^əl/ US: /ɪnˈfæləbəl/ ,(in fal′ə bəl)

WordReference Random House Learner's Dictionary of American English © 2025

in•fal•li•ble /ɪnˈfæləbəl/   adj. 

1. absolutely sure:
   an infallible rule.
2. that never fails in operating; certain:
   had an infallible remedy for the hiccups.
3. not fallible;
   free from error, as applied to persons, their judgment, or what they say:
   thought he was infallible.

in•fal•li•bil•i•ty/ɪnˌfæləˈbɪlɪti/  in•fal•li•ble•ness, n. 

[uncountable] They believe in the infallibility of the Pope in faith and morals.

in•fal•li•bly, adv. 

WordReference Random House Unabridged Dictionary of American English © 2025

in•fal•li•ble  (in fal′ə bəl), adj. 

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. Religion [Rom. Cath. Ch.] 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.

n. 

5. an infallible person or thing.

• Medieval Latin infallibilis. See in-³, fallible
• late Middle English 1375–1425

in•fal′li•bil′i•ty, in•fal′li•ble•ness, n. 
in•fal′li•bly, adv. 
Synonyms

• 1, 2. See reliable. 

Collins Concise English Dictionary © HarperCollins Publishers::

infallible / ɪnˈfæləb^əl/ adjective

1. not fallible; not liable to error
2. not liable to failure; certain; sure: an infallible cure

noun

1. a person or thing that is incapable of error or failure

inˌfalliˈbility, inˈfallibleness noun

inˈfallibly adverb