quintillion

from WordNet (r) 3.0 (2006)

quintillion
    n 1: the number that is represented as a one followed by 18
         zeros

from The Free On-line Dictionary of Computing (8 July 2008)

quintillion

   10^30 in Europe (this is called a {nonillion} in the United
   States and Canada).

   10^18 in the United States and Canada (this is called a
   trillion in Europe).

   [Collins dictionary].