amphibian vs natatory

amphibian

adj
  • Of or relating to the class Amphibia. 

  • Capable of operating on both land and water amphibious. 

noun
  • A vehicle which can operate on land and water. See Wikipedia article on "Amphibious aircraft" 

  • An animal of the Amphibia; any four-legged vertebrate that does not have amniotic eggs, living both on land and in water. 

natatory

adj
  • of, or relating to, swimming 

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