hydraulic vs pelagic

hydraulic

adj
  • Pertaining to water. 

  • Related to, or operated by, hydraulics. 

verb
  • To mine using the technique of hydraulic mining. 

pelagic

adj
  • Of or pertaining to oceans. 

  • Living in the open sea rather than in coastal or inland waters. 

noun
  • Any organism that lives in the open sea rather than in coastal or inland waters. 

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