An onomatopoeia is a word that phonetically resembles the sound it is intended to represent. The word "onomatopoeia" itself is derived from Greek and means "making or creating names." This type of literary device is used to make the text more vivid, particularly since it is difficult to describe a sound within the limitations of the written page and standard English. Let's now look at some examples of onomatopoeias within Lord of the Flies...

In Chapter One, Ralph is dancing around and pretending to be a fighter-plane on the beach. He pretends to machine-gun Piggy, and makes the noise "Sche-aa-ow!" while diving into the sand by Piggy's feet.

In Chapter Seven, Maurice agrees that Ralph has hit a boar with a spear, and describes the noise as, "Wheee!" 

In Chapter Eleven, someone is tossing stones by Ralph's head, and the noise is described as, "a faint 'Zup'!"