Source : Webster's Revised Unabridged Dictionary (1913)

Trillion \Tril"lion\, n. [F. trillion, formed from the pref.
   tri- in imitation of million a million. Cf. {Billion}.]
   According to the French notation, which is used upon the
   Continent generally and in the United States, the number
   expressed by a unit with twelve ciphers annexed; a million
   millions; according to the English notation, the number
   produced by involving a million to the third power, or the
   number represented by a unit with eighteen ciphers annexed.
   See the Note under {Numeration}.

Source : WordNet®

trillion
     adj 1: one quintillion in Great Britain [syn: {a trillion}]
     2: one million million in the United States [syn: {a trillion}]

trillion
     n 1: the number that is represented as a one followed by 18
          zeros; "in England they call a quintillion a trillion"
          [syn: {one million million million}]
     2: the number that is represented as a one followed by 12
        zeros; "in England they call a trillion a billion" [syn: {one
        million million}, {1000000000000}]

Source : Free On-Line Dictionary of Computing

trillion
     
         In Britain, France, and Germany, 10^18 or a
        million cubed.
     
        In the USA and Canada, 10^12.
     
        [Elsewhere?]
     
        (1996-10-03)