onomatopœia

from The Century Dictionary.

• noun In philology, the formation of names by imitation of natural sounds; the naming of anything by a more or less exact reproduction of the sound which it makes, or something audible connected with it; the imitative principle in language-making: thus, the verbs buzz and hum and the nouns pewit, whippoorwill, etc., are produced by onomatopœia.
• noun In rhetoric, the use of imitative and naturally suggestive words for rhetorical effect.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Philol.) The formation of words in imitation of sounds; a figure of speech in which the sound of a word is imitative of the sound of the thing which the word represents

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Alternative spelling of onomatopoeia.