The term 'OLDEN INSTRUMENT' can be broken down into two crossword solutions: REBEC (5 letters) and SPINET (6 letters). A rebec is a bowed string instrument that was popular in Europe during the Middle Ages and Renaissance. It has three strings and a pear-shaped body. A SPINET is a type of harpsichord that was popular in the Baroque period. It is smaller than a regular harpsichord and has a single keyboard. Both the rebec and the SPINET are examples of olden instruments that were used in classical music.