The term RELATIVE OF A CELLO can be solved by two different crossword solutions: VIOLA (5 letters) and VIOL (4 letters). The VIOLA is a stringed instrument that is similar to the violin, but slightly larger in size. It is tuned a fifth lower than the violin and is considered to be the alto voice of the string family. The VIOL is an even larger version of the VIOLA and is tuned an octave lower than the violin. Both instruments are used in orchestras and chamber music ensembles.