Source : Webster's Revised Unabridged Dictionary (1913)

Sextillion \Sex*til"lion\, n. [Formed (in imitation of million)
   fr. L. sextus sixth, sex six: cf. F. sextilion.]
   According to the method of numeration (which is followed also
   in the United States), the number expressed by a unit with
   twenty-one ciphers annexed. According to the English method,
   a million raised to the sixth power, or the number expressed
   by a unit with thirty-six ciphers annexed. See {Numeration}.