The term 'KEY MATERIAL Piano' is composed of three crossword solutions: EBONY (5 letters), KEY (3 letters), and MATERIAL (8 letters). EBONY is a type of hardwood, usually black or dark brown in color, that is used to make furniture and musical instruments such as pianos. KEY is a noun that can refer to a physical object, such as a KEY to a door, or a figurative concept, such as the KEY to success. MATERIAL is a noun that refers to the substances or objects from which something is made. In this case, it could refer to the wood used to make a piano.