The term 'Grand Instrument' is a reference to the PIANO, which is a five-letter word. The PIANO is a musical instrument that has been around since the 1700s and is one of the most popular instruments in the world. It is a keyboard instrument that produces sound when its keys are pressed. The strings of the PIANO are struck by hammers when the keys are pressed, producing a unique sound. The PIANO is used in many genres of music, from classical to jazz to pop.