infallible (adj.)

"exempt from error in judgment, knowledge, or opinion," early 15c., from Medieval Latin infallibilis, from in- "not, opposite of" (see in- (1)) + Late Latin fallibilis (see fallible). In reference to Popes, attested from 1870, hence infallibilism, the doctrine of this; infallibilist. Related: Infallibly.

Origin and meaning of infallible

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Definitions of infallible from WordNet

infallible (adj.)
incapable of failure or error;
an infallible memory
the Catholic Church considers the Pope infallible
no doctor is infallible
an infallible antidote