billion vs gajillion

billion

noun
  • An unspecified very large number. 

  • a thousand million (logic: 1,000 × 1,000^2): 1 followed by nine zeros, 10⁹; a milliard 

gajillion

noun
  • An unspecified large number (of); a gazillion. 

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