cardinal number
 (pl. trillions or (with numeral or quantifying word) same)
  - a million million (1,000,000,000,000 or 1012). 
▸Brit. dated a million million million (1,000,000,000,000,000,000 or 1018).
 - 
(trillions)
 informal a very large number or amount.
 
 
  Derivative
  
    
      - trillionth ordinal number.
 
    
   
  Etymology
  C17: from Fr., from million, by substitution of the prefix tri- ‘three’ for the initial letters.