The word 'zither' is derived from Latin cythara, which was used in this form for the title covers on many 16th and 17th century German printed manuscript books originally for the 'cittern' – from the Greek word kithara, an instrument used in Ancient Greece. The German scholar Michael Praetorius described a small English cittern as a Klein Englisch Zitterlein in his treatise Syntagma Musicum, published during the early 17th century, recording the language consonant shift. It is not fully understood how 'zitter' or 'zither' came to be applied to the instruments in this article as well as German varieties of the cittern. Other types of zither also existed in Germany, mostly drone zithers like the scheitholt (which was mentioned by Praetorius) or hummel, but these generally have their own individual regional names and may have been in use before the introduction into the lexicon of 'cythara' and its German derivative cognate.
The Hornbostel-Sachs system, an academic instrument classification method, also uses the term zither to classify all stringed instruments in which the strings do not extend beyond the sounding box. This includes such diverse instruments as the hammered dulcimer, psaltery, Appalachian dulcimer, guqin, guzheng, tromba marina, koto, gusli, kanun, kanklės, kantele, kokles, valiha, gayageum, đàn tranh, autoharp, santoor, yangqin, santur, swarmandal, and others. Pedal steel guitars, lap guitars (where the neck serves no separate function other than to extend the string length), and keyboard instruments like the clavichord, harpsichord and piano also fall within this broad categorical use.
The word has also been used in conjunction with brand varieties of other string instruments, for example the zither banjo.