The term 'fizzling out' can be described as DYING, which is a 5 letter word. Fizzling out is a phrase used to describe a situation that is gradually coming to an end. It is often used to describe a situation that is losing momentum or enthusiasm. For example, a project that is fizzling out may have started off with a lot of energy and excitement, but over time the enthusiasm has died down and the project is no longer progressing.