a·corn (??kôrn?, ??k?rn)n. The fruit of an oak, consisting of a single-seeded, thick-walled nut set in a woody, cuplike base.[Middle English akorn, from Old English æcern.]Word History: A thoughtful glance at the word acorn might produce the surmise that it is made up of oak (from Old English ?c) and corn, especially if we think of corn in its sense of “a kernel or seed of a plant,” as in peppercorn. The fact that others thought the word was so constituted partly accounts for the present form acorn. Here we see the workings of the process of linguistic change known as folk etymology, an alteration in form of a word or phrase so that it resembles a more familiar term mistakenly regarded as analogous. Acorn actually goes back to Old English æcern, “acorn,” which in turn goes back to the Indo-European root *?g-, meaning “fruit, berry.”American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.acorn (?e?k??n) n (Botany) the fruit of an oak tree, consisting of a smooth thick-walled nut in a woody scaly cuplike base[C16: a variant (through influence of corn) of Old English æcern the fruit of a tree, acorn; related to Gothic akran fruit, yield]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014a?corn (?e? k?rn, ?e? k?rn) n. the typically ovoid fruit or nut of an oak, enclosed at the base by a cupule. [before 1000; Middle English acorne (influenced by corn1), akern, Old English æcern, æcren mast, c. Middle High German ackeran acorn, Old Norse akarn fruit of wild trees, Gothic akran fruit, yield] a?corned, adj. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.