quadrillion

n. [ F., fr. L. quater four times, akin to quattuor four, E. four; -- formed like million. See Four, Million. ] According to the French notation, which is followed also upon the Continent and in the United States, a unit with fifteen ciphers annexed; according to the English notation, the number produced by involving a million to the fourth power, or the number represented by a unit with twenty-four ciphers annexed. See the Note under Numeration. [ 1913 Webster ]