gazebo vs pergola

gazebo

noun
  • A belvedere, either a type of summer-house or a roofed, detached porch-like structure, usually in a yard, park or lawn. 

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 gazebo and pergola occurred in a corpus of books? (source: Google Ngram Viewer )