Etymology
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fallible (adj.)
early 15c., from Medieval Latin fallibilis "liable to err, deceitful," literally "that can be deceived," from Latin fallere "deceive" (see fail (v.)).
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infallible (adj.)
Origin and meaning of infallible
"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.
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