| Septillion (n.) According to the French method of numeration (which is followed also in the United States), the number expressed by a unit with twenty-four ciphers annexed. According to the English method, the number expressed by a unit with forty-two ciphers annexed. See Numeration. Thesaurus Entries astronomical number, billion, decillion, duodecillion, googolplex, infinitude, infinity, jillion, large number, nonillion, novemdecillion, octillion, octodecillion, quadrillion, quattuordecillion, quindecillion, quintillion, septillion, sexdecillion, sextillion, tredecillion, trillion, undecillion, vigintillion, zillion |