by 1939, arbitrary coinage, modeled on million, etc.
(also gadzillion or gillion or kajillion or skillion or zillion or quadzillion) A great many; an indefinitely large number; scads: a jillion jackpots/ The beautiful people who would be at her cocktail party (''A zillion horny studs!'')/ All those years we paid no official notice to those gadzillions of Chinese/ This instant, in fact, quadzillions of these particles may be streaking harmlessly through our bodies (1940s+)