Gittern is a derived word from guitar and this, same time, from greek kitara.
It names a plucked chordophone of the short-neck lutes family, vastly represented during the Middle Ages in stone carvings as well as in beautiful paintings by authors like Jaume Serra, Juan Oliver or Simone Martini. Looking at its stringing, and its plectrum technique, we can assume that it would be used mostly for accompanying the voice. It was a monoxile instrument, which could include, or not, a sickle-shaped pegbox and topped with a carved animal head.
Gittern based on Cantiga de Sta. María ner. 90, by Alfonso X “The Wise”. V.L.: 420 mm.
Juan Oliver, 1330. Pamplona Cathedral.
Cantigas de Santa María
We can check how there were a large number of guitar minstrels in (mostly spanish) 15th century courts. We can highlight some documents found by Higini Anglés in 1970, dated in Olite in February the 2nd of 1405, and which is a Charles IIIrd's accounting receipt, showing payments to Hans de Loge and Johan de Palencia, guitar and lute players. The same king payed, in 1414, Alfonso de Carrión, Alonso de Toledo and Martín de Toledo, guitarists in Olite all of them. Another well-known guitarist was Rodriguet de la Guitarra, who appears in documents from the Courts of Ferdinand I and Alfonso V of Aragón, in 1415, and Juan II in 1417. He's supposed to be the author of "Angellorum psallat tripudium" ballad, from Codex Chantilly.