The psaltery is an old stringed instrument, a member of the zither family, which is like the dulcimer in that it consists of a sound box over which tuned strings are stretched, however these are plucked instead of struck. In that it is a stringed box with strings, it can be considered a forerunner of the harpsichord.
The term “psaltery”, from the Latin “psalterium”, reveals its perceived similarity with the instrument of the psalms in medieval times. It was widely used in the Middle Ages but was unsuitable for the more sophisticated music developing during the early Renaissance and lost favour to the dulcimer and the lute.
Reference: “The Grove Concise Dictionary of Music”