natatory vs seawater

natatory

adj
  • of, or relating to, swimming 

seawater

adj
  • Associated in some way with seawater, or intended for dealing with seawater. 

  • Consisting of seawater. 

noun
  • The saltwater of a sea or ocean. 

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