Third World (n.)
1963, from French tiers monde, formulated 1952 by French economic historian Alfred Sauvy (1898-1990) on model of the third estate (French tiers état) of Revolutionary France; his first world (The West) and second world (the Soviet bloc) never caught on.
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Anno Domini 

"in the year of the Christian era," 1570s, Latin, literally "in the year of (our) Lord," from ablative of annus "year" (see annual (adj.)) + Late Latin Domini, genitive of Dominus "the Lord" (see domain). Also see A.D.

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Kyrie eleison 
early 13c., a Greek liturgical formula adopted untranslated into the Latin mass, literally "lord have mercy" (Psalms cxxii.3, Matthew xv.22, xvii.15, etc.). From kyrie, vocative of kyrios "lord, master" (see church (n.)) + eleeson, aorist imperative of eleo "I have pity on, show mercy to," from eleos "pity, mercy" (see alms). Hence, the corresponding part of a musical setting of the Mass or Anglican Communion.
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compos mentis (adj.)

Latin, literally "in command of one's mind," from compos "having the mastery of," from com "with, together" (see com-) + stem of potis "powerful, master" (from PIE root *poti- "powerful; lord"), + mentis, genitive of mens "mind" (from PIE root *men- (1) "to think").

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Ahura Mazda 

the God of Zoroastrianism, from Avestan ahura- "spirit, lord," from Indo-Iranian *asuras, from suffixed form of PIE root *ansu- "spirit" (see Aesir) + Avestan mazda- "wise," from PIE *mens-dhe- "to set the mind" (from root *men- (1) "to think" + root *dhe- "to set, put").

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ivory tower (n.)

symbol of artistic or intellectual aloofness, by 1889, from French tour d'ivoire, used in 1837 by critic Charles-Augustin Sainte-Beuve (1804-1869) with reference to the poet Alfred de Vigny (1797-1863), whom he accused of excessive aloofness.

Et Vigny, plus secret, comme en sa tour d'ivoire, avant midi rentrait. [Sainte-Beuve, "Pensées d'Août, à M. Villemain," 1837]

Used earlier as a type of a wonder or a symbol of "the ideal." The literal image is perhaps from Song of Solomon [vii:4]:

Thy neck is as a tower of ivory; thine eyes like the fishpools in Heshbon, by the gate of Bathrabbim: thy nose is as the tower of Lebanon which looketh toward Damascus. [KJV]
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name borne by two rulers of Tenochtitlan in ancient Mesoamerica, from Spanish Moctezuma, from Nahuatl (Aztecan) Moteuczoma, said to mean "he who frowns like a lord" or "he who is angry in a noble manner." Montezuma's revenge, "severe intestinal infection" sometimes suffered by non-natives in Mexico, is by 1962, in reference to Montezuma II (1466-1520), Aztec ruler at the time of the Spanish arrival and conquest of Mexico.

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absolute zero (n.)
"lowest possible temperature which the nature of heat admits" (determined to be –273 centigrade, –458 Fahrenheit), the idea dates back to 1702 and its general value was guessed to within a few degrees soon thereafter, but not precisely discovered until Lord Kelvin's work in 1848. It was known by many names, such as infinite cold, absolute cold, natural zero of temperature; the term absolute zero was among them by 1806.
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legem pone (n.)
"payment of money, cash down," 1570s, old slang, from the title in the Anglican prayer-book of the psalm appointed for Matins on the 25th of the month; it was consequently associated especially with March 25, the new year of the old calendar and a quarter day, when payments and debts came due and money changed hands generally. The title is from the first two words of the fifth division of Psalm cxix: Legem pone mihi, Domine, viam justificationum tuarum "Teach me, O Lord, the way of thy statutes."
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Three Rs (n.)

1824; said to have been given as a toast by Sir William Curtis (1752-1829), a beloved lord mayor of London in the 1820s, who seems to have been a figure of fun to whom many mangled phrases were attributed. Among the toasts he is alleged to have given at public dinners were "The Female Ladies of London;" "The three C's—Cox, King, and Curtis;" and "The three R's—Reading, Writing, and Rithmetic."

It has been very much the fashion amongst a class of persons to attribute to Sir W. C. ... a vulgarity and ignorance of speech which are by no means consistent with his character and conduct. The worthy and hospitable baronet has a rapid mode of speech, but it is always correct ; and although some eccentricities are mixed up in his composition, he is highly honourable, and has been a very useful member of society, particularly to his London constituents. [The Mirror, Jan. 29, 1825]

After listing some examples, the article continues:

It is, however, very certain, that at a city festival some years ago, having indulged very freely, he fell asleep, when some wag, choosing to consider him dead, wrote his epitaph, which was found next morning pinned to the baronet's dress coat:—
"Here lies the great Curtis,
Of London, Lord May'r:
He's left this here world,
And gone to that there."
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