We're looking for a twelve-letter word. Such words aren't very common, but they are far too common to find a particular one in a list of 12-letter words. It's a compound word. Although the riddle doesn't exactly say so, the word becomes two smaller words when we separate it into 3 and 9 letters or into 4 and 8 letters.

The 9-letter word is synonymous with massacre and carnage. The 8-letter word is the sound of mirth. It is really a remarkable transformation from 3-9 to 4-8.