The term 'LONG TUBE' can be solved by the word 'PIPE', which is a four-letter word. A PIPE is a tube-like structure that is used to transport liquids, gases, and other materials from one place to another. It is usually made of metal, plastic, or other materials and is often used in plumbing and construction. Pipes are also used in many industrial applications, such as oil and gas production, water treatment, and chemical processing.