onomatopoeia

onomatopoeia
(I just learned this one! It's pronounced like on-o-mato-pia)

The naming of a thing or action with a vocal imitation of the sound associated with it;
as in, 
"There's a word for that?!"
"Mmmhmm. There sure is!" 
(note "mmhmm")

Other words that are onomatopoeic would be buzz or hiss. 
Can you come up with any yourself?