The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

subtract
    v 1: make a subtraction; "subtract this amount from my paycheck"
         [syn: subtract, deduct, take off] [ant: add, add
         together]
    2: take off or away; "this prefix was subtracted when the word
       was borrowed from French"