mainmast vs topgallant

mainmast

noun
  • The tallest mast of a sailing ship that has more than one mast; particularly a full-rigged ship. 

topgallant

noun
  • The sail suspended from the topmost section of a mast. 

  • The topmost section of a mast; topgallant mast. 

  • Anything elevated or splendid. 

adj
  • Situated above the topmast and below the royal mast. 

  • Of the most superior quality; the best of its kind. 

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