1265 Juan Gil of Zamora mentions the early guitar in "Ars Musica.
The guitar's roots are in Spain. Realistically, it cannot be traced back further than the 15th Century. It is thought to have been invented by the people of Malaga. This early instrument was a "four course" guitar, from which the ukulele is derived. The first guitars were very small, and were originally strung with four pair of strings. Each pair was call a course.
The word "guitar" was brought into English as an adaptation of the Spanish word "guitarra," which was, in turn, derived from the Greek "kithara." Tracing the roots of the word further back into linguistic history, it seems to have been a combination of the Indo-European stem "guit-," meaning music, and the root "-tar," meaning chord or string. The root "-tar" is actually common to a number of languages, and can also be found in the word "sitar," also a stringed musical instrument. Although the spelling and pronunciation differs between languages, these key elements are present in most words for "guitar" throughout history.