estuary vs ostium

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. 

ostium

noun
  • The mouth of a river. 

  • A small opening or orifice, as in a body organ or passage. 

  • Any of the small openings or pores in a sponge. 

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