The etymology of apple
The below is excerpted from The Diner’s Dictionary.
The apple was probably the earliest of all fruits to be cultivated by human beings. Its wild ancestor was a sharp, mouth-puckering little thing, like today’s crab apple, and this abel-, as our Indo-European ancestors called it, no doubt needed sweetening with honey. But as it spread through northern Europe, taking its name with it (German Apfel, Dutch appel, Swedish äpple, Gothic apel, Russian jabloko, Lithuanian óbuolas, Welsh afal, English apple), it grew larger, redder, and sweeter (the Romans introduced cultivated apples into Britain). The southern European languages have, by and large, not distinguished too clearly between words for ‘apple’ and words for ‘fruit’ in general, a clear sign of the apple’s centrality: Greek melon, for instance, source of English melon and Latin mālum, signified any fruit as well as specifically ‘apple’, and Latin pōmum, source of French pomme ‘apple’, meant ‘fruit’. It is no coincidence that the fruit of the tree of the knowledge of good and evil in the Garden of Eden, which Adam and Eve ate with such disastrous consequences, and which is not specifically named in Genesis, has come to be identified in popular culture as an apple.
Getting to the core of apple metaphors
A sure indication of the apple’s antiquity is the number of metaphors it has gathered about itself. The apple of someone’s eye was originally the pupil, so-called because it was once thought to be spherical, but the phrase’s figurative application to ‘someone or something much loved’ dates back at least to King Alfred’s time. In Australian English, she’s apples means ‘everything’s fine’ (it was originally rhyming slang—apples and rice ‘nice’); and of course Cockney rhyming slang has apples and pears—or just apples for short—for ‘stairs’. The use of ‘the Big Apple’ as a sobriquet of New York City goes back to 1920, when the American racing journalist John J. FitzGerald heard two stable hands in New Orleans use the phrase to refer to the racetracks of New York (perhaps with the underlying idea of an apple being a toothsome treat, as a win in New York would be for out-of-towners). He used it in print in that sense in 1921, and by 1924 he had expanded its reference to cover the city of New York itself. It achieved some general currency after that, and was in fairly wide use by the 1940s. It was revived and popularized in the early 1970s as part of a publicity campaign for the city. ‘The Big Apple’ was also the name given to a type of jazz dance popular in the late 1930s: ‘It was an earthquake, a trembler. California was doing the Big Apple!’, Ellery Queen, The Four of Hearts (1938).
Check out more apple idioms and phrases.