ebb vs retrocession

ebb

noun
  • The receding movement of the tide. 

  • A European bunting, the corn bunting (Emberiza calandra, syns. Emberiza miliaria, Milaria calandra). 

  • A gradual decline. 

  • A low state; a state of depression. 

adj
  • low, shallow 

verb
  • to fish with stakes and nets that serve to prevent the fish from getting back into the sea with the ebb 

  • To cause to flow back. 

  • to flow back or recede 

  • to fall away or decline 

retrocession

noun
  • The act of retroceding; a going back. 

  • The transfer of risk from one reinsurer to another. 

  • The return of land, rights, etc. previously ceded. 

  • Metastasis of an eruption or tumour from the surface to the interior of the body. 

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