fault (n.)

late 13c., faute, "deficiency," from Old French faute, earlier falte, "opening, gap; failure, flaw, blemish; lack, deficiency" (12c.), from Vulgar Latin *fallita "a shortcoming, falling," from Latin falsus "deceptive, feigned, spurious," past participle of fallere "deceive, disappoint" (see fail (v.)).

The -l- was restored 16c., probably in imitation of Latin, but the letter was silent until 18c. Sense of "physical defect" is from early 14c.; that of "moral culpability" (milder than sin or vice, but more serious than an error) is first recorded late 14c. Geological sense is from 1796. The use in tennis (c. 1600) is closer to the etymological sense.

fault (v.)

"find fault with," mid-15c. from fault (n.). Earlier it was used in an intransitive sense of "be deficient" (late 14c., Scottish). Related: Faulted; faulter; faulting.

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Definitions of fault from WordNet
fault (n.)
a wrong action attributable to bad judgment or ignorance or inattention;
I could understand his English in spite of his grammatical faults
Synonyms: mistake / error
fault (n.)
an imperfection in an object or machine;
Synonyms: defect / flaw
fault (n.)
the quality of being inadequate or falling short of perfection;
he knew his own faults much better than she did
Synonyms: demerit
fault (n.)
(geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other;
they built it right over a geological fault
he studied the faulting of the earth's crust
Synonyms: faulting / geological fault / shift / fracture / break
fault (n.)
(electronics) equipment failure attributable to some defect in a circuit (loose connection or insulation failure or short circuit etc.);
it took much longer to find the fault than to fix it
fault (n.)
responsibility for a bad situation or event;
it was John's fault
fault (n.)
(sports) a serve that is illegal (e.g., that lands outside the prescribed area);
he served too many double faults
fault (v.)
put or pin the blame on;
Synonyms: blame