Glycerin Start is a term used to describe the process of starting an internal combustion engine with a mixture of glycerin and nitro, which is a five-letter word. This method of starting an engine was developed in the early 1900s and is still used today. The glycerin helps to create a spark that ignites the fuel, while the nitro helps to increase the combustibility of the fuel. This combination of glycerin and nitro is used to start engines in a variety of applications, including cars, boats, and airplanes.