Etymology
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savoir-faire (n.)

"instinctive knowledge of the right course of action in any circumstance, faculty of knowing just what to do and how to do it," 1815 (Scott), a French phrase in English, literally "to know (how) to do," from savoir "to know" (from Latin sapere; see sapient) + faire (from Latin facere "to make, do;" from PIE root *dhe- "to set, put"). French also has savoir-vivre "knowledge of and ability in the usages of polite society; knowledge of customs in the world," which turns up in English writers, occasionally, in italics.

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courteous (adj.)

c. 1300, curteis, "having elegant manners, well-bred, polite, urbane," also "gracious, benevolent," from Old French curteis (Modern French courtois) "having courtly bearing or manners," from curt "court" (see court (n.)) + -eis, from Latin -ensis.

Rare before c. 1500. In feudal society, also denoting a man of good education (hence the name Curtis). Medieval courts were associated with good behavior and also beauty; compare German hübsch "beautiful," from Middle High German hübesch "beautiful," originally "courteous, well-bred," from Old Franconian hofesch, from hof "court." Related: Courteously (mid-14c., kurteis-liche).

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mister 

as a conventional title of courtesy before a man's Christian name, mid-15c., unaccented variant of master (n.), but without its meaning. As a form of address when the man's name is unknown (often with a tinge of rudeness), from 1760.

The disappearance of master and mister, and the restricted and obsolescent use of sir, as an unaccompanied term of address, and the like facts with regard to mistress, Mrs., and madam, tend to deprive the English language of polite terms of address to strangers. Sir and madam or ma'am as direct terms of address are old-fashioned and obsolescent in ordinary speech, and mister and lady in this use are confined almost entirely to the lower classes. [Century Dictionary, 1895]
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smooth (adj.)
Old English smoð "smooth, serene, calm," variant of smeðe "free from roughness, not harsh, polished; soft; suave; agreeable," of unknown origin and with no known cognates. Of words, looks, "pleasant, polite, sincere" late 14c., but later "flattering, insinuating" (mid-15c.). Slang meaning "superior, classy, clever" is attested from 1893. Sense of "stylish" is from 1922.

Smooth-bore in reference to guns is from 1812. smooth talk (v.) is recorded from 1950. A 1599 dictionary has smoothboots "a flatterer, a faire spoken man, a cunning tongued fellow." The usual Old English form was smeðe, and there is a dialectal smeeth found in places names, such as Smithfield, Smedley.
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manners (n.)

"external behavior (especially polite behavior) in social intercourse," late 14c., plural of manner in a specific sense of "proper behavior, commendable habits of conduct" (c. 1300).

Under bad manners, as under graver faults, lies very commonly an overestimate of our special individuality, as distinguished from our generic humanity. [Oliver W. Holmes, "The Professor at the Breakfast Table," 1858]

Earlier it meant "moral character" (early 13c.).

MANNERS-BIT, a portion of a dish left by the guests that the host may not feel himself reproached for insufficient preparation. [Rev. Joseph Hunter, "The Hallamshire Glossary," 1829]
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pregnant (adj.1)

"with child, impregnated, that has conceived in the womb," early 15c., from Latin praegnantem (nominative praegnans, originally praegnas) "with child," literally "before birth," probably from prae- "before" (see pre-) + root of gnasci "be born" (from PIE root *gene- "give birth, beget").

The word tended to be avoided in polite conversation until c. 1950; modern euphemisms include anticipating, enceinte, expecting, in a family way, in a delicate (or interesting) condition. Old English terms included mid-bearne, literally "with child;" bearn-eaca, literally "child-adding" or "child-increasing;" and geacnod "increased." Among c. 1800 slang terms for "pregnant" was poisoned (in reference to the swelling).

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must (v.)

auxiliary of prediction, "be obliged, be necessarily impelled," from Old English moste, past tense of motan "have to, be able to," from Proto-Germanic *motanan (source also of Old Saxon motan "to be obliged to, have to," Old Frisian mota, Middle Low German moten, Dutch moeten, German müssen "to be obliged to," Gothic gamotan "to have room to, to be able to"), perhaps from PIE root *med- "take appropriate measures," but this old suggestion lately has been doubted. Used as present tense from c. 1300, eventually displacing motan, from the custom of using past subjunctive as a moderate or polite form of the present.

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lie (n.1)

"an untruth; conscious and intentional falsehood, false statement made with intent to deceive," Old English lyge, lige "lie, falsehood," from Proto-Germanic *lugiz (source also of Old Norse lygi, Danish løgn, Old Frisian leyne (fem.), Dutch leugen (fem.), Old High German lugi, German Lüge, Gothic liugn "a lie"), from the root of lie (v.1).

To give the lie to "accuse directly of lying" is attested from 1590s. Lie-detector is recorded by 1909.

In mod. use, the word is normally a violent expression of moral reprobation, which in polite conversation tends to be avoided, the synonyms falsehood and untruth being often substituted as relatively euphemistic. [OED]
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jape (v.)
late 14c., "to trick, beguile, jilt; to mock," also "to act foolishly; to speak jokingly, jest pleasantly," perhaps from Old French japer "to howl, bawl, scream" (Modern French japper), of echoic origin, or from Old French gaber "to mock, deride." Phonetics suits the former, but sense the latter explanation. Chaucer has it in the full range of senses. Around mid-15c. the Middle English word took on a slang sense of "have sex with" and subsequently vanished from polite usage. It was revived in the benign sense of "say or do something in jest" by Scott, etc., and has limped along since in stilted prose. Related: Japed; japing.
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mistress (n.)

c. 1300, "female teacher, governess; supervisor of novices in a convent," from Old French maistresse "mistress (lover); housekeeper; governess, female teacher" (Modern French maîtresse), fem. of maistre "master," from Latin magister "chief, head, director, teacher" (see master (n.)).

Sense of "a woman who employs others or has authority over a household and servants" is from early 15c. Meaning "woman who has mastered an art or branch of study" is from mid-15c. Sense of "kept woman of a married man" is from early 15c. As a polite form of address to a woman, mid-15c. Meaning "woman who is beloved and courted, one who has command over a lover's heart" is from c. 1500.

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