acoustic guitar vs guitar

acoustic guitar

noun
  • A hollow-body guitar of the older variety, in contradistinction to an electric guitar. 

guitar

noun
  • Any type of musical instrument of the lute family, characterized by a flat back, along with a neck whose upper surface is in the same plane as the soundboard, with strings along the neck and parallel to the soundboard. 

  • A stringed musical instrument, of European origin, usually with a fretted fingerboard and six strings, played with the fingers or a plectrum (guitar pick). 

verb
  • To play the guitar. 

How often have the words acoustic guitar and guitar occurred in a corpus of books? (source: Google Ngram Viewer )