1. 
[syn: remainder, balance, residual, residue, residuum, rest]
The Collaborative International Dictionary of English v.0.48:
Residuum \Re*sid"u*um\ (-?m), n. [L. See Residue.]
   That which is left after any process of separation or
   purification; that which remains after certain specified
   deductions are made; residue.
   [1913 Webster]
         "I think so," is the whole residuum . . . after
         evaporating the prodigious pretensions of the zealot
         demagogue.                               --L. Taylor.
   [1913 Webster]
WordNet (r) 3.0 (2006):
residuum
    n 1: something left after other parts have been taken away;
         "there was no remainder"; "he threw away the rest"; "he
         took what he wanted and I got the balance" [syn:
         remainder, balance, residual, residue, residuum,
         rest]