Acorn comes from Old English æcern ('fruit of the wild; mast'), from Proto-Germanic akraz ('fruit of the unenclosed land'); into Middle English aker ('nut, fruit of the oak'), reshaped by folk association with oak and corn into Modern English acorn ('oak nut'). In current use it is a noun meaning "the nut of the oak tree, typically rounded and held in a rough, scaly cupule". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The history is mainly one of transmission into English, with the older form and sense carried through borrowing or adaptation. For dictionary purposes, the important point is the continuity between the older form, the route into English, and the present lexical sense.