Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

subtrahend
     n : the number to be subtracted from the minuend