Guitar definition – according to the encyclopedia of the year 1974 /with footnotes/:
Guitar – [a word of Spanish origin, Greek] it is a musical instrument from the group of lute-type plucked chordophones (let's mark, if anyone has no idea what it is, this does not eliminate him from learning to play the guitar – reminds the author).
Ma 6 strings tuned according to notes: E, A, d g, h, e1. Plucked with fingers, less often a plectrum (I assume, it's a feather).
It appeared in Europe in the Middle Ages, gained particular popularity in the 18th and 19th centuries. Currently used in entertainment bands, often replaced by an electric guitar, equipped with an electromagnetic transducer.