Once meant any fruit — 'pineapple' was originally a pinecone, and only English kept the name for the tropical fruit.
The round fruit of a tree of the rose family, which typically has thin green or red skin and crisp flesh.
From Old English 'æppel' (apple, any fruit, fruit in general, even an eye — the 'apple' of the eye), from Proto-Germanic *aplaz (apple, fruit), from PIE *h₂ébōl (apple). In Old English, 'æppel' did not mean exclusively what we now call an apple — it meant any fruit. A cucumber was an 'eorþæppel' (earth-apple), a banana was a 'finger-apple' in some medieval texts, and