buoy vs lightship

buoy

noun
  • A float moored in water to mark a location, warn of danger, indicate a navigational channel or for other purposes 

  • A life-buoy; a life preserver. 

verb
  • To maintain or enhance enthusiasm or confidence; to lift the spirits of. 

  • To support or maintain at a high level. 

  • To keep afloat or aloft; used with up. 

  • To mark with a buoy. 

lightship

noun
  • A vessel riding at anchor and displaying a light for the guidance of sailors, in a position where a fixed lighthouse structure would be impracticable. 

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