The term 'orchestra string' refers to a group of instruments that are played with a bow, such as the violin, viola, cello, and double bass. The four-letter solution for this term is 'VIOL, ' which is an abbreviation for the violin. The violin is the smallest and highest-pitched instrument in the orchestra string family, and it is often used as a solo instrument. The other instruments in the orchestra string family are the viola, cello, and double bass, which are larger and lower-pitched than the violin. All of these instruments are played with a bow and are essential components of any orchestra.