1670s, from French quadrillion (16c.) from quadri- "four" (from PIE root *kwetwer- "four") + (m)illion. Compare billion. In Great Britain, the fourth power of a million (1 followed by 24 zeroes); in the U.S., the fifth power of a thousand (1 followed by 15 zeroes).
Thomas Hope, first of the family to possess the Deepdene, was the author of "Anastasius," a book of the same class as Beckford's "Vathek." In each case a millionaire (we shall soon have billionaires, trillionaires, quadrillionaires) fettered, imprisoned, by abject opulence, strove to reveal himself to the world through a romance. [Mortimer Collins, "A Walk Through Surrey," Temple Bar, August 1866]