O.E. æppel “apple,” from P.Gmc. *ap(a)laz (cf. O.Fris., Du. appel, O.N. eple, O.H.G. apful, Ger. Apfel), from PIE *ab(e)l “apple” (cf. Gaul. avallo, O.Ir. ubull, Lith. obuolys, O.C.S. jabloko), but the exact relation and original sense of these is uncertain. Gk. melon and L. malum are probably from a pre-I.E. Mediterranean language. A generic term for all fruit, other than berries but including nuts, as late as 17c., hence its use for the unnamed “fruit of the forbidden tree” in Genesis. Cucumbers, in one O.E. work, are eorþæppla, lit. “earth-apples” (cf. Fr. pomme de terre “potato,” lit. “earth-apple;” see also melon). Fr. pomme is from L. pomum “fruit.”
“A roted eppel amang þe holen, makeþ rotie þe yzounde.” [“Ayenbite of Inwit,” 1340]
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 (O.E.), 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.