Disappearing Sounds is a term used to describe the gradual decrease in the volume of sound over time. This phenomenon is often caused by environmental factors such as wind, temperature, and humidity. The term can also be used to describe the gradual disappearance of certain sounds from language over time. The crossword solution for this term is 'POOFS', which is an onomatopoeia for a sudden, sharp sound. This sound is often used to describe the sound of something disappearing quickly.