Source : Webster's Revised Unabridged Dictionary (1913)

Dilution \Di*lu"tion\, n. [Cf. F. dilution.]
   The act of diluting, or the state of being diluted.
   --Arbuthnot.

Source : WordNet®

dilution
     n 1: a diluted solution
     2: weakening (reducing the concentration) by the addition of
        water or a thinner [ant: {concentration}]