subtractionn.[L. subtractio a drawing back. See Subtract, and cf. Substraction.]1. The act or operation of subtracting or taking away a part.()2. (Math.) The taking of a lesser number or quantity from a greater of the same kind or denomination; an operation for finding the difference between two numbers or quantities.()3. (Law) The withdrawing or withholding from a person of some right to which he is entitled by law.()(Blackstone.)