infallible (adj) – incapable of error; without fault
BREAKDOWN: IN- (not) + FAL- (fail) + -IBLE (able to)
— fallible means capable of failure or of making a mistake; likely to fail
This word is built on the root FAL-, which means to fail or to deceive.
Common FAL- words include fault, fail, failure, false, and falsehood.
More esoteric FAL- words include fallibility.