- The definition of an acorn is a round nut with a wood-like cap that comes from an oak tree.
An example of an acorn is a nut that a squirrel eats once it has fallen from the oak tree.
A variety of squash named for its acorn like shape.
Two acorn nuts with oak leaves.
acorn definition by Webster's New World
Origin: Middle English akorn ; from Old English æcern, nut, mast of trees; akin to Gothic akran, Old Norse akarn ; from Indo-European base an unverified form əg-, to grow, fruit: form influenced, influence by associated, association with Old English ac, oak plush corn, grain
acorn definition by American Heritage Dictionary
Origin: Middle English akorn, from Old English ǽcern.Word History: A thoughtful glance at the word acorn might produce the surmise that it is made up of oak 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 ǽcern, “acorn,” which in turn goes back to the Indo-European root *ōg-, meaning “fruit, berry.”