Sagan vs gillion

Sagan

noun
  • A unit of measurement equal to at least four billion. 

name
  • A village in Sardasht Rural District, in the Central District of Bashagard County, Hormozgan Province, Iran. 

  • A town in southern Ethiopia, named for the river. 

  • A river in southern Ethiopia. 

  • A surname. 

gillion

noun
  • An unspecified large number (of). 

num
  • A thousand million, proposed as an alternative to the (now little used) British milliard and the (ambiguous, in the UK) US billion. 

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