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"

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "subtract":
   abate, abrade, abrupt, abstract, add, algebraize, alienate, bate,
   calculate, cast, cast off, cast out, cipher, compute, curtail,
   cut adrift, cut off, cut out, decrease, deduct, delete, depart,
   depreciate, derogate, detract, detract from, diminish,
   disarticulate, disconnect, discount, disengage, disjoin, disjoint,
   disparage, dissociate, disunite, divide, divorce, dope out, drain,
   draw back, eat away, eject, erode, estimate, estrange, expel,
   extract, extract roots, figure, figure in, figure out, file away,
   impair, isolate, knock, leach, leave, lessen, measure, multiply,
   part, pull away, pull back, pull out, purify, reckon, reduce,
   refine, remove, retrench, rub away, score, segregate, separate,
   sequester, set apart, set aside, shorten, shut off, split,
   stand aloof, stand apart, stand aside, step aside, subduct,
   take account of, take away, take away from, take from, take off,
   take out, tally, thin, thin out, throw off, throw out, uncouple,
   unyoke, wear away, weed, withdraw, work out