The term INSTRUMENT FOR A MARX is a four-letter word, 'HARP'. The HARP is a stringed instrument that has been around for centuries. It is one of the oldest known instruments and is believed to have originated in ancient Egypt. The HARP is also associated with the Marx Brothers, a comedy troupe from the early 20th century. The Marx Brothers often used the HARP as a comedic prop in their films and stage performances.