canal vs moat

canal

verb
  • To travel along a canal by boat 

  • To dig an artificial waterway in or to (a place), especially for drainage 

noun
  • A tubular channel within the body. 

  • An artificial waterway or artificially improved river used for travel, shipping, or irrigation. 

  • One of the faint, hazy markings resembling straight lines on early telescopic images of the surface of Mars. 

moat

verb
  • To surround with a moat. 

noun
  • A clear ring outside the eyewall of a tropical cyclone. 

  • An aspect of a business which makes it more "defensible" from competitors, because of the nature of its products, services or franchise or for some other reason. 

  • A circular lowland between a resurgent dome and the walls of the caldera surrounding it. 

  • A deep, wide defensive ditch, normally filled with water, surrounding a fortified habitation. 

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