The crossword solution for the term 'Dangerous Thing to Run On' is EMPTY, which is a five-letter word. This phrase can refer to a variety of things, but it is most commonly used to describe a situation where someone is running on EMPTY in terms of energy or resources. It can also be used to describe a situation where someone is running on fumes, meaning they are running out of time or money. In either case, it is a dangerous thing to run on because it can lead to exhaustion, financial ruin, or other negative consequences.