It's a what???

The other week we went to a Chinese buffet with some friends of ours. Christiana was sitting next to one of our friends and asked if he would like to play hangman. He agreed, and she quickly drew the gallows and carefully counted out the number of letters in her word.
After a guessing a few letters, our friend decided that he needed a hint.
"What kind of word is it? Is it a noun or verb?" He asked.
Chrissy responded, "It's an onomatopoeia."