æcern

Old English æcern was a general word for tree fruit, particularly the mast — the nuts and fruits that fell from forest trees and fed pigs. It had nothing to do with oaks specifically, and nothing to do with corn. The folk etymology that splits acorn into 'oak' + 'corn' is wrong, though it has been repeated since at least the 16th century. The resemblance is coincidence, and the coincidence reshaped the word.

The deeper etymology points to Proto-Germanic *akran, meaning 'fruit of the unenclosed land' — wild fruit, as opposed to cultivated crops. Gothic akran meant simply 'fruit.' Old High German ackeran meant 'fruit of the forest.' The word described anything that grew without being planted. Only in English did it narrow to mean the fruit of one specific tree.

The narrowing happened because oaks dominated the English landscape, and their mast was the most economically important wild crop. Pigs fattened on acorns. The right to collect acorns — pannage — was a legal privilege in medieval English forest law. The Domesday Book of 1086 records forests valued by how many pigs their acorns could feed. When æcern narrowed to mean 'oak fruit,' it was because the oak's fruit mattered more than any other tree's.

The spelling shifted too. By Middle English, æcern had become akerne, then acorne, and finally acorn — the final form influenced by the false association with oak and corn. The folk etymology did not just explain the word; it changed it. People heard what they expected to hear, and the spelling followed the mishearing. The real history — a Germanic word for wild fruit — was buried under a more satisfying but incorrect story.