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).

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.

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] 

 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).

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.

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

late 13c., "crystallized sugar," from Old French çucre candi "sugar candy," ultimately from Arabic qandi, from Persian qand "cane sugar," probably from Sanskrit khanda "piece (of sugar)," perhaps from Dravidian (compare Tamil kantu "candy," kattu "to harden, condense").

The sense gradually broadened (especially in U.S.) to mean by late 19c. "any confection having sugar as its basis." In Britain these are sweets, and candy tends to be restricted to sweets made only from boiled sugar and striped in bright colors. A candy-pull (1865) was a gathering of young people for making (by pulling into the right consistency) and eating molasses candy.

"preserve or encrust with sugar," 1530s, from candy (n.). Related: Candied; candying.

also eye candy, "attractive woman on a TV show, etc.," by 1978, based on a metaphor also found in nose candy "cocaine" (1930).

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).

"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.

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."

"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.

old name for "tomato," 1570s, translating French pomme d'amour, corresponding to German Liebesapfel, etc., but the alleged aphrodisiac qualities that supposedly inspired the name seem far-fetched. The phrase also has been explained as a mangled transliteration of the Italian name pomo d'oro (by 1560s), taken as from adorare "to adore," but probably rather from d'or "of gold" (the earliest tomatoes brought to Italy in the mid-1500s apparently were of the yellow or orange variety), or, less likely, pomo de'Mori or Spanish pome dei Moro, literally "Moorish apple."

also applesauce, by 1739, American English, from apple + sauce (n.). The 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.