Source : Free On-Line Dictionary of Computing

gillion
     
         /gil'y*n/ or /jil'y*n/ (From {giga-} by analogy with
        mega/million and tera/trillion) 10^9.
     
        Same as an American billion or a British "milliard".  How one
        pronounces this depends on whether one speaks {giga-} with a
        hard or soft "g".
     
        [{Jargon File}]
     
        (1995-03-17)