The term 'Piano Relative' can be solved by two crossword solutions: ORGAN (5 letters) and CELESTA (7 letters). The ORGAN is a keyboard instrument that produces sound by blowing air through pipes. It has been around since ancient times and is still used in churches and other venues today. The celesta is a modern instrument that was invented in the late 19th century. It is similar to a piano, but produces a softer, more delicate sound. Both instruments are related to the piano, but have their own unique characteristics.