appleyoudaoicibaDictYouDict[apple 词源字典]
apple: [OE] Words related to apple are found all over Europe; not just in Germanic languages (German apfel, Dutch appel, Swedish äpple), but also in Balto-Slavonic (Lithuanian óbuolas, Polish jabtko), and Celtic (Irish ubhall, Welsh afal) languages. The Old English version was æppel, which developed to modern English apple.

Apparently from earliest times the word was applied not just to the fruit we now know as the apple, but to any fruit in general. For example, John de Trevisa, in his translation of De proprietatibus rerum 1398 wrote ‘All manner apples that is, “fruit” that are enclosed in a hard skin, rind, or shell, are called Nuces nuts’. The term earth-apple has been applied to several vegetables, including the cucumber and the potato (compare French pomme de terre), and pineapple (which originally meant ‘pine cone’, with particular reference to the edible pine nuts) was applied to the tropical fruit in the 17th century, because of its supposed resemblance to a pine cone.
[apple etymology, apple origin, 英语词源]
apple (n.)youdaoicibaDictYouDict
Old English æppel "apple; any kind of fruit; fruit in general," from Proto-Germanic *ap(a)laz (cognates: Old Saxon, Old Frisian, Dutch appel, Old Norse eple, Old High German apful, German Apfel), from PIE *ab(e)l "apple" (cognates: 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. ["The Heart of Islam: Enduring Values for Humanity," Seyyed Hossein Nasr, 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 of something that upsets the apple cart is attested from 1788. Road apple "horse dropping" is from 1942.