the.com/acoustic guitar

means A guitar that makes its sound purely from the vibration of its strings resonating through a hollow wooden body, with no electronic amplification needed.

from 'Guitar' traces back through French and Spanish guitarra to the Greek kithara, an ancient plucked instrument whose name also gave us 'zither.' 'Acoustic' comes from Greek akoustikos, 'of hearing,' from akouein, 'to hear.' The two words didn't need to share a sentence until the 20th century, when electric guitars arrived and someone had to specify, almost apologetically, that the old wooden kind still worked by nothing more than air and ears.