The term MUSICAL INSTRUMENT; TUBE can be solved by the four letter word PIPE. A PIPE is a type of musical instrument that produces sound when air is blown through it. It is usually made of metal or wood and has several holes along its length. The player blows into one end of the PIPE, and the sound is produced by the vibration of the air inside the PIPE. Pipes are used in many different types of music, from traditional folk music to modern jazz.