Etymology
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apple (n.)

Old English æppel "apple; any kind of fruit; fruit in general," from Proto-Germanic *ap(a)laz (source also of Old Saxon, Old Frisian, Dutch appel, Old Norse eple, Old High German apful, German Apfel), from PIE *ab(e)l- "apple" (source also of Gaulish avallo "fruit;" Old Irish ubull, Lithuanian obuolys, Old Church Slavonic jabloko "apple"), but the exact relation and original sense of these is uncertain (compare melon).

A roted eppel amang þe holen, makeþ rotie þe yzounde. ["Ayenbite of Inwit," 1340]

In Middle English and as late as 17c., it was a generic term for all fruit other than berries but including nuts (such as Old English fingeræppla "dates," literally "finger-apples;" Middle English appel of paradis "banana," c. 1400). Hence its grafting onto the unnamed "fruit of the forbidden tree" in Genesis. Cucumbers, in one Old English work, are eorþæppla, literally "earth-apples" (compare French pomme de terre "potato," literally "earth-apple;" see also melon). French pomme is from Latin pomum "apple; fruit" (see Pomona).

As far as the forbidden fruit is concerned, again, the Quran does not mention it explicitly, but according to traditional commentaries it was not an apple, as believed by Christians and Jews, but wheat. [Seyyed Hossein Nasr, "The Heart of Islam: Enduring Values for Humanity," 2002]

Apple of Discord (c. 1400) was thrown into the wedding of Thetis and Peleus by Eris (goddess of chaos and discord), who had not been invited, and inscribed kallisti "To the Prettiest One." Paris, elected to choose which goddess should have it, gave it to Aphrodite, offending Hera and Athene, with consequences of the Trojan War, etc.

Apple of one's eye (Old English), symbol of what is most cherished, was the pupil, supposed to be a globular solid body. Apple-polisher "one who curries favor" first attested 1928 in student slang. The image in the phrase upset the apple cart "spoil the undertaking" is attested from 1788. Road-apple "horse dropping" is from 1942.

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apple-tree (n.)

Old English æpeltreow; see apple + tree (n.). Another name for it was Old English apuldore, which survived into Middle English and is preserved in place names (Appledore).

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apple-pie (n.)
1580s, from apple + pie; noted by 1893 as a typical American dish. Apple-pie bed as a name for a childish prank is recorded from 1781; supposedly from the way of making apple turnovers, but some think it a folk etymology of French nappe pliée "folded sheet."
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apple-sauce (n.)
also applesauce, by 1739, American English, from apple + sauce (n.). Slang meaning "nonsense" is attested from 1921 and was noted as a vogue word early 1920s. Mencken credits it to cartoonist T.A. ("Tad") Dorgan. DAS suggests the word was thus used because applesauce was cheap fare served in boardinghouses.
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applejack (n.)
also apple-jack, "apple-brandy, liquor distilled from cider," 1816, from apple + jack (n.).
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berry (n.)
Old English berie "berry, grape," from Proto-Germanic *basjom (source also of Old Norse ber, Middle Dutch bere, German Beere "berry;" Old Saxon winberi, Gothic weinabasi "grape"), which is of unknown origin. This and apple are the only native fruit names.
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pineapple (n.)

late 14c., pin-appel, "pine cone," from pine (n.) + apple. The reference to the fruit of the tropical plant (from resemblance of shape) is recorded by 1660s, and pine-cone emerged 1690s to replace pineapple in its original sense except in dialect. For "pine-cone," Old English also used pinhnyte "pine nut." Pine-apple also was used in a late 14c. Biblical translation for "pomegranate."

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Adam's apple (n.)
bulge in the throat caused by the cartilage of the larynx, 1731, corresponding to Latin pomum Adami, perhaps an inexact translation of Hebrew tappuah haadam, literally "man's swelling," from ha-adam "the man" + tappuah "anything swollen." The reference is to the legend that a piece of the forbidden fruit (commonly believed to have been an apple) that Eve gave Adam stuck in his throat. It is more prominent in men than women. The term is mentioned early 15c. as the name of an actual oriental and Mediterranean fruit, a variety of lime with an indentation fancied to resemble the marks of Adam's teeth.
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Big Apple (n.)
"New York City," 1909 (but popularized by 1970s tourism promotion campaign), apparently from jazz musicians' use of apple for any city, especially a Northern one.
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