The term 'MA'S INSTRUMENT' is a crossword solution for the word 'CELLO', which is a five-letter string instrument of the violin family. The CELLO is a bowed string instrument with four strings tuned in perfect fifths. It is played by sitting and holding the instrument between the knees, with the left hand controlling the strings and the right hand moving the bow. The CELLO has a deep, rich sound and is often used as a solo instrument or in chamber music.