fallible (adj.)Related entries & more
early 15c., from Medieval Latin fallibilis "liable to err, deceitful," literally "that can be deceived," from Latin fallere "deceive" (see fail (v.)).
infallible (adj.)Related entries & more
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."exempt from error in judgment, knowledge, or opinion," early 15c., from Medieval Latin