[ in-fal-uh-buhl ]
See synonyms for: infallibleinfallibilityinfallibly on

  1. absolutely trustworthy or sure: an infallible rule.

  2. unfailing in effectiveness or operation; certain: an infallible remedy.

  1. not fallible; exempt from liability to error, as persons, their judgment, or pronouncements: an infallible principle.

  2. 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.

  1. an infallible person or thing.

Origin of infallible

First recorded in 1375–1425; late Middle English word from Medieval Latin word infallibilis.See in-3, fallible

synonym study For infallible

1, 2. See reliable.

Other words from infallible

  • in·fal·li·bil·i·ty, in·fal·li·ble·ness, noun
  • in·fal·li·bly, adverb
  • non·in·fal·li·ble, adjective
  • non·in·fal·li·bly, adverb Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use infallible in a sentence

British Dictionary definitions for infallible


/ (ɪnˈfæləbəl) /

  1. not fallible; not liable to error

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

  1. completely dependable or trustworthy

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

Derived forms of infallible

  • infallibility or infallibleness, noun
  • infallibly, adverb

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012