The term 'disappearance sound of' can be completed with four different solutions in a crossword puzzle: POOF (4 letters), PFFT (4 letters), MOONSET (7 letters), HOFFA (5 letters), and ASTA (4 letters). POOF is an onomatopoeia that is used to describe the sound of something disappearing quickly, such as a puff of smoke. PFFT is another onomatopoeia that is used to describe the sound of something disappearing suddenly, such as a balloon popping. MOONSET is the disappearance of the moon from the sky, usually at night. HOFFA is a reference to Jimmy Hoffa, an American labor union leader who mysteriously disappeared in 1975. ASTA is a reference to the dog in the 1934 film The Thin Man, who was known for his disappearing acts.