Source : Webster's Revised Unabridged Dictionary (1913)

Subtract \Sub*tract"\, v. t. [imp. & p. p. {Subtracted}; p. pr.
   & vb. n. {Subtracting}.] [L. subtractus, p. p. of subtrahere
   to draw from beneath, withdraw, remove; sub under + trahere
   to draw. See {Trace}, v. t., and cf. {Substract}.]
   To withdraw, or take away, as a part from the whole; to
   deduct; as, subtract 5 from 9, and the remainder is 4.

Source : WordNet®

subtract
     v : make a subtraction [syn: {deduct}, {take off}] [ant: {add}]