Etymology
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black swan (n.)

proverbial for "something extremely rare or non-existent" (late 14c.) is from Juvenal ["Sat." vi. 164], but the real thing turned up in Australia (Chenopsis atratus).

"Do you say no worthy wife is to be found among all these crowds?" Well, let her be handsome, charming, rich and fertile; let her have ancient ancestors ranged about her halls; let her be more chaste than all the dishevelled Sabine maidens who stopped the war—a prodigy as rare upon the earth as a black swan! yet who could endure a wife that possessed all perfections? I would rather have a Venusian wench for my wife than you, O Cornelia, mother of the Gracchi, if, with all your virtues, you bring me a haughty brow, and reckon up Triumphs as part of your marriage portion. [Juvenal]

Blue dahlia also was used 19c. for "something rare and unheard of."

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bel canto 
1894, Italian, literally "fine song." See belle + chant.
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rara avis (n.)

c. 1600, "peculiar person, person of a type seldom encountered," from Latin rara avis, literally "strange bird," from rara, fem. of rarus "rare" (see rare (adj.1)) + avis "bird" (see aviary). Latin plural is raræ aves. A phrase used of Horace's peacock (a Roman delicacy), Juvenal's black swan ("Rara avis in terris, nigroque simillima cygno"). A figure perhaps natural to the superstitious Romans, who divined by bird-watching.

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lang syne 
"long ago," c. 1500, Scottish dialect variant of long since; popularized in Burns' song, 1788. Century Dictionary has langsyner "person who lived long ago."
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Tin Pan Alley (n.)
"hit song writing business," 1907, from tin pan, slang for "a decrepit piano" (1882). The original one was "that little section of Twenty-eighth Street, Manhattan, that lies between Broadway and Sixth Avenue," home to many music publishing houses.
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rock and roll (n.)
also rock 'n' roll, 1954 in reference to a specific style of popular music, from rock (v.2) + roll (v.). The verbal phrase had been an African-American vernacular euphemism for "sexual intercourse," used in popular dance music lyrics and song titles at least since the 1930s.
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pina colada (n.)

"long drink made with pineapple juice, rum, and coconut," 1923, from Spanish piña colada, literally "strained pineapple." The first word was originally "pine-cone" (and formerly pinna), from Latin pinea (see pineapple). Second word ultimately is from Latin colare "to strain" (see colander). Ayto ("Diner's Dictionary") writes that the drink probably originated in Puerto Rico and "enjoyed a certain vogue in the mid to late 1970s," as evidenced by a certain song.

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black sheep (n.)
by 1822 in figurative sense of "member of some group guilty of offensive conduct and unlike the other members," supposedly because a real black sheep had wool that could not be dyed and thus was worth less. But one black sheep in a flock was considered good luck by shepherds in Sussex, Somerset, Kent, Derbyshire. First known publication of Baa Baa Black Sheep nursery rhyme is in "Tommy Thumb's Pretty Song Book" (c. 1744).
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teddy bear (n.)

1906, named for U.S. president Theodore "Teddy" Roosevelt (1858-1919), a noted big-game hunter, whose conservationist fervor inspired a comic illustrated poem in the New York Times of Jan. 7, 1906, about two bears named Teddy, whose names were transferred to two bears presented to the Bronx Zoo that year. The name was picked up by toy dealers in 1907 for a line of "Roosevelt bears" imported from Germany. Meaning "big, lovable person" first attested 1957, from the song popularized by Elvis Presley.

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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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