infallible

adjective

in·​fal·​li·​ble (ˌ)in-ˈfa-lə-bəl 

1

: incapable of error : unerring

an infallible memory

2

: not liable to mislead, deceive, or disappoint : certain

an infallible remedy

3

: incapable of error in defining doctrines touching faith or morals

infallibility

(ˌ)in-ˌfa-lə-ˈbi-lə-tē 

noun

infallibly

(ˌ)in-ˈfa-lə-blē 

adverb

Did you know?

Watch out when you hear about infallible predictions, an infallible plan, an infallible cure, or even infallible lip gloss. Infallible isn't a claim that scientists, engineers, and doctors like to make, so you're probably getting better information when the word not comes first. You may have heard the phrase "papal infallibility", which refers to the official position of the Roman Catholic church, adopted in the 19th century, that certain solemn statements made by a Pope about faith or morals were not to be questioned. Popes since then have been careful not to make many of these statements.

Synonyms of infallible

• unerring
• perfect
• reliable
• flawless
• unfailing

Examples of infallible in a Sentence

I never claimed to be infallible.

There is no infallible remedy to these problems.

Recent Examples on the Web

If play is the show’s law, the infallible resilience of family structure is its moral core. —Jean Garnett, New Yorker, 18 Apr. 2026

Despite the show’s insistence that Robby is flawed, he’s also portrayed as medically infallible. —Kathryn Vanarendonk, Vulture, 17 Apr. 2026

Note that mmWave tech isn’t infallible, however. —New Atlas, 26 Feb. 2026

Trump remains popular among his base and remarkably infallible in the eyes of his loyalist administration and still commands extraordinary deference from many leaders in his party. —Kevin Rector, Los Angeles Times, 25 Feb. 2026

Word History

Etymology

Middle English, from Medieval Latin infallibilis, from Latin in- + Late Latin fallibilis fallible

First Known Use

15th century, in the meaning defined at sense 1

Rhymes for infallible

• fallible

Kids Definition

infallible

adjective

in·​fal·​li·​ble (ˈ)in-ˈfal-ə-bəl 

1

: not capable of being wrong : unerring

an infallible memory

2

: not likely to fail : sure

an infallible remedy

infallibility

(ˌ)in-ˌfal-ə-ˈbil-ət-ē 

noun

infallibly

(ˈ)in-ˈfal-ə-blē 

adverb