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]WordNet (r) 3.0 (2006):
subtrahend n 1: the number to be subtracted from the minuend