The term 'Sound of Disappearance' can be summarized by two crossword solutions: PFFT (4 letters) and POOF (4 letters). These words are both onomatopoeic, meaning they imitate the sound of a particular action. PFFT is used to describe a sudden burst of air or a puff of smoke, while POOF is used to describe a cloud of dust or smoke that appears suddenly and then quickly dissipates. Both words are commonly used to describe the sound of something disappearing.