rafter vs summer (tree)

rafter

verb
  • To furnish (a building) with rafters. 

  • To make (timber, etc.) into rafters. 

  • To plough so as to turn the grass side of each furrow upon an unploughed ridge; to ridge. 

noun
  • A raftsman. 

  • A flock of turkeys. 

  • One of a series of sloped beams that extend from the ridge or hip to the downslope perimeter or eave, designed to support the roof deck and its associated loads. 

summer (tree)

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