arbor vs pergola

arbor

noun
  • A shady sitting place or pergola usually in a park or garden, surrounded by climbing shrubs, vines or other vegetation. 

  • A grove of trees. 

  • A spindle of a wheel. 

  • A bar for supporting cutting tools. 

  • An axis or shaft supporting a rotating part on a lathe. 

pergola

noun
  • Such a framework employed to provide shade, especially over a patio. 

  • A framework in the form of a passageway of columns that supports a trelliswork roof; used to support and train climbing plants. 

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