zither, stringed musical instrument, derived from the psaltery and the dulcimer. It has a flat sound box over which are stretched from 30 to 45 strings; these are plucked with the fingers and a plectrum. In the 18th cent. one or both sides began to be curved to produce greater sonority. The term zither is also used generically for various instruments, including the dulcimer, the psaltery, and several Asian instruments. The dulcimer in use in the Kentucky mountains is, in fact, a zither.