Etymology
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impertinent (adj.)

late 14c., "unconnected, unrelated, not to the point" (now obsolete; OED's last citation is from Coleridge), from Old French impertinent (14c.) or directly from Late Latin impertinentem (nominative impertinens) "not belonging," literally "not to the point," from assimilated form of Latin in- "not, opposite of" (see in- (1)) + pertinens (see pertinent). Sense of "rudely bold, uncivil, offensively presumptuous" is from 1680s, from earlier sense of "not appropriate to the situation" (1580s), which probably is modeled on similar use in French, especially by Molière, from notion of meddling in what is beyond one's proper sphere.

Impertinent means forward, intrusive, generally from curiosity but sometimes with undesired advice, etc.; officious means forward to offer and undertake service where it is neither needed nor desired. A busybody may be either impertinent or officious, or both. [Century Dictionary]
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impertinently (adv.)
mid-15c., "not to the point, irrelevantly," from impertinent + -ly (2). Meaning "intrusively, presumptuously" is from 1640s.
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impertinence (n.)
c. 1600, "incivility," from French impertinence, from impertinent (see impertinent). Meaning "irrelevance" is from 1620s. Impertinency is from 1580s as "a triviality, an absurdity."
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saucily (adv.)

"impudently, with impertinent boldness," 1540s; see saucy + -ly (2).

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slack-jawed (adj.)
1882, "over-talkative," from slack-jaw (n.) "impertinent language" (1797), from slack (adj.) + jaw (n.). Meaning "open-mouthed and speechless" from astonishment, stupidity, etc., is from 1905.
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inept (adj.)
c. 1600, "not fit or suitable, inapt," also "absurd, foolish," from French inepte "incapable" (14c.) or directly from Latin ineptus "unsuitable, improper, impertinent; absurd, awkward, silly, tactless," from in- "not, opposite of" (see in- (1)) + aptus "apt" (see apt). Related: Ineptly; ineptness.
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jackanapes (n.)

mid-15c., "a monkey," also "an impertinent, conceited fellow, an absurd fop," a general term of reproach (in mid-15c. especially a contemptuous nickname for William de la Pole, Duke of Suffolk), of unknown origin. Apparently from Jack of Naples, but whether this is some specific personification of Jack (which is attested from 16c. as "saucy or impertinent fellow") or folk etymology of jack (n.) + ape (n.) is unknown. See extensive note in OED. Century Dictionary suggests "orig., it is supposed, a man who exhibited performing apes." Farmer and Henley ("Slang and Its Analogues") say "originally, no doubt, a gaudy-suited and performing ape." Its fem. counterpart is Jane-of-apes (Massinger) "a pert, forward girl."

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backtalk (n.)
also back-talk, "impertinent retort," 1833; see back (adv.) + talk (n.). Originally often used in literary attempts at Irish or Scottish idiom. To talk back "answer impudently or rudely" is from 1849.
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presumptuous (adj.)

mid-14c., "arrogant, overweening, impertinent, going beyond the limits of propriety or good sense in thought or conduct," from Old French presuntuex, presontuos, presumptueuse (12c.; Modern French présomptueux) and directly from Late Latin praesumptuosus "full of boldness," a variant of praesumptiosus, from past participle stem of Latin praesumere "anticipate," in Late Latin, "assume" (see presume). Related: Presumptuously; presumptuousness.

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saucy (adj.)

c. 1500, "resembling sauce" (a sense now obsolete), later, of persons, words, etc., "impertinent in speech or conduct, flippantly bold, cheeky" (1520s), from sauce (n.) + -y (2). The connecting notion is sauce in the figurative sense of "that which adds intensity, piquancy in words or actions."

Compare Skelton's have eaten sauce for "be abusive." Also compare sauce malapert "impertinence" (1520s), and sauce (n.) in its obsolete use as a vocative for "impudent person" (1530s).  In Shakespeare, with overtones of "wanton, lascivious," it was "a term of serious condemnation" [OED]. Also compare salty in similar senses.

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