acoustic guitar
US /əˌkuː.stɪk ɡɪˈtɑːr/
UK /əˌkuː.stɪk ɡɪˈtɑːr/

1.
a guitar that produces sound by means of vibrating strings and a hollow resonating body, without electrical amplification
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He played a beautiful melody on his acoustic guitar.
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Many folk songs are best performed with an acoustic guitar.