lute-like musical instrument, 1620s, from French guitare, which was altered by Spanish and Provençal forms from Old French guiterre, earlier guiterne, from Latin cithara, from Greek kithara "cithara," a triangular seven-stringed musical instrument related to the lyre, perhaps from Persian sihtar (see sitar).
In post-classical times, the ancient instrument developed in many varieties in different places, keeping a local variant of the old name or a diminutive of it. Some of these local instruments subsequently became widely known, and many descendants of kithara reached English in reference to various stringed, guitar-like instruments: citole, giterne (both early 14c.), gittern, cithern (1560s), cittern (1590s), cither (c. 1600), guitar, and zither.
Modern guitar also is directly from Spanish guitarra (14c.), which ultimately is from the Greek. The Arabic word is perhaps from Spanish or Greek, though often the relationship is said to be the reverse. The modern guitar is one of a large class of instruments used in all countries and ages but particularly popular in Spain and periodically so in France and England. Other 17c, forms of the word in English include guittara, guitarra, gittar, and guitarre.