| Quadrillion (n.) 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 Numeration. Thesaurus Entries a billion, a crore, a lakh, a million, a myriad, a nonillion, a quadrillion, a thousand, a zillion, decillion, duodecillion, googol, googolplex, jillion, nonillion, novemdecillion, octillion, octodecillion, quattuordecillion, quindecillion, quintillion, septillion, sexdecillion, sextillion, tredecillion, trillion, undecillion, vigintillion, zillion | ![]() |