estuary vs seawater

estuary

noun
  • An ocean inlet also fed by fresh river water. 

  • A coastal water body where ocean tides and river water merge, resulting in a brackish water zone. 

seawater

noun
  • The saltwater of a sea or ocean. 

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

  • Consisting of seawater. 

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