The word 'apple' descends from Old English 'æppel,' from Proto-Germanic *aplaz, from PIE *h₂ébōl (apple). It is one of the oldest fruit-words in the Indo-European family, with cognates spanning from Celtic (Welsh 'afal,' Irish 'úll') to Balto-Slavic (Lithuanian 'obuolys,' Old Church Slavonic 'ablŭko') to Germanic (German 'Apfel,' Dutch 'appel,' Old Norse 'epli'). The wide distribution suggests the PIE speakers were familiar with wild apples, which are native to Central Asia.
The most important etymological fact about 'apple' is that in Old English, it did not mean exclusively the fruit of Malus domestica. 'Æppel' was a generic word for fruit — any fruit, and sometimes for round objects in general. A date could be an 'æppel.' A cucumber was an 'eorþæppel' (earth-apple). The 'apple of the eye' (Old English 'æppel' of the eye) referred to the pupil — the round, apple-like sphere of the eyeball. This generic sense survives in several modern languages: French
The story of 'pineapple' perfectly illustrates the old generic sense. In Middle English, a 'pineapple' was a pinecone — the 'apple' (fruit) of the pine tree. When European explorers encountered the tropical fruit Ananas comosus in the Americas, they called it 'pineapple' because it resembled a large pinecone. Nearly every other European language borrowed the Tupi (indigenous Brazilian) word 'ananas' for the fruit — French 'ananas,' Spanish 'ananá,' German 'Ananas,' Portuguese 'ananás,' Italian 'ananas.' English alone
The forbidden fruit in the Garden of Eden is never identified as an apple in the Hebrew Bible — the text says only 'the fruit of the tree.' The association of the apple with the Fall likely arose from a Latin pun: the Latin word for 'evil' is 'malum,' and the Latin word for 'apple' is 'mālum.' The near-homophony (differing only in vowel length) may have encouraged medieval artists and theologians to depict the fruit of the knowledge of good and evil as an apple. Jerome's Vulgate translation, which used 'malum' in both senses, would have reinforced the association.
The name of the city Almaty (former capital of Kazakhstan) means 'father of apples' in Kazakh, and the region around Almaty is believed to be the original homeland of Malus domestica. The wild apple forests of the Tian Shan mountains in Central Asia are the genetic source of all cultivated apple varieties. The word 'apple,' through its PIE root *h₂ébōl, may thus have originated geographically close to where the fruit itself originated biologically — a rare case of a word and its referent sharing an ancestral homeland.