The term CELLO'S ANCESTOR is composed of two crossword solutions: VIOL (4 letters) and CIDER (5 letters). The first solution, VIOL, is an abbreviation for the stringed instrument known as the viola da gamba, which is a precursor to the modern cello. The second solution, CIDER, is an abbreviation for the cittern, a plucked string instrument that was popular in the 16th and 17th centuries. Both instruments are considered to be ancestors of the cello, which was developed in the late 17th century.