adj. 1. Incapable of erring: an infallible guide; an infallible source of information. 2. Incapable of failing; certain: an infallible antidote; an infallible rule. 3. Roman Catholic Church Incapable of error in expounding doctrine on faith or morals. [Middle English, from Medieval Latin īnfallibilis : Latin in-, not; see IN-1 + Medieval Latin fallibilis, fallible; see FALLIBLE.] in·fal′li·bili·ty, in·falli·ble·ness n. in·falli·bly adv. |
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.