Instruments similar to what we now know as the guitar weren't just from the 1930s and 1940s - they are a piece of ancient history, and have been popular for at least 5,000 years. It appears to be derived from earlier instruments known in ancient central Asia.
Instruments very similar to the guitar appear in ancient carvings and statues recovered from Susa, Iran. The modern word, guitar, is from Spanish, and possibly from the earlier Greek word kithara.
Prospective sources for various names of musical instruments that guitar could be derived from all appear to be a combination of two Indo-European roots: guit-, similar to Sanskrit sangeet meaning "music", and -tar a widely attested root meaning "chord" or "string".
The word guitar may also be a Persian loanword to Iberian Arabic. The word qitara is an Arabic name for various members of the lute family that preceded the Western guitar. The name guitar was introduced into Spanish when guitars were brought into Iberia by the Moors after the 10th century. (related article).
The Spanish vihuela, a guitar-like instrument of the 15th and 16th centuries is, due to its many similarities, considered to be an intermediate form of the ancestral guitar and the modern guitar, with lute-style tuning and a small, guitar-like body. It enjoyed only a short period of popularity as it was superseded by the guitar. The Ancient Iranian lute, tar, is also in the word guitar.
The electric guitar was invented by Adolph Rickenbacher, with the help of George Beauchamp and Paul Berth, in 1931. Rickenbacher was the inventor of the horseshoe-magnet pickup. However, it was Danelectro that first produced electric guitars for the public, and also pioneered tube amp technology.
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