Etymology
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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.
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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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no-fault (adj.)
as a type of U.S. motor vehicle insurance, 1967, from no + fault (n.).
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fault-finding (n.)
1620s, from verbal phrase find fault (with) (late 14c.); see fault (n.) + find (v.). Related: Fault-finder (1560s).
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faulty (adj.)
"containing faults, errors, or defects," late 14c., from fault (n.) + -y (2). Related: Faultily; faultiness.
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faultless (adj.)
mid-14c., "having no blemishes or imperfections," from fault (n.) + -less. Meaning "having no blame, culpability, or guilt" is from 1570s. Related: Faultlessly; faultlessness.
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vault (n.1)
"arched roof or ceiling," c. 1300, vaute, from Old French voute "arch, vaulting, vaulted roof or chamber," from Vulgar Latin *volta, contraction of *volvita, noun use of fem. of *volvitus, alteration of Latin volutus "bowed, arched," past participle of volvere "to turn, turn around, roll," from PIE root *wel- (3) "to turn, revolve." The -l- appeared in English c. 1400, an etymological insertion in imitation of earlier forms (compare fault (n.), assault (n.)).
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assault (n.)
late 14c., earlier asaut (c. 1200), "physical attack (on a person), sudden violent onslaught (on a place)," from Old French asaut, assaut "an attack, an assault, attacking forces" (12c.), from Vulgar Latin *adsaltus "attack, assault," from ad "to" (see ad-) + Latin saltus "a leap," from salire "to leap, spring" (see salient (adj.)). The -l- was restored, as in fault (n.), vault (n.1). In law by 1580s; historically, assault includes menacing words or actions coupled with present means to effect them; battery is an actual blow.
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begrudge (v.)
late 14c., bigrucchen, "grumble over, find fault, show dissatisfaction," especially "envy the possession of," from be- + Middle English grucchen "to murmur, find fault with, be angry" (see grudge). Related: Begrudged; begrudging; begrudgingly.
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emend (v.)
"remove faults from, alter for the better," c. 1400, from Latin emendare "to free from fault, correct, improve, revise," from assimilated form of ex "out" (see ex-) + mendum (nominative menda) "fault, blemish" (see amend). Related: Emended; emending.
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