gillion vs thousand million

gillion

num

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

noun

  • An unspecified large number (of). 

thousand million

num

  • Synonym of billion (sense 1) 

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