subtrahend

from WordNet (r) 3.0 (2006)

subtrahend
    n 1: the number to be subtracted from the minuend

from The Collaborative International Dictionary of English v.0.48

Subtrahend \Sub"tra*hend`\, n. [L. subtrahendus that is to be
   subtracted, p.fut.pess. of subtrahere. See {Subtract}.]
   (Math.)
   The sum or number to be subtracted, or taken from another
   (the {minuend}) to find the {difference}.
   [1913 Webster + PJC]