The Collaborative International Dictionary of English v.0.48:

Hydrolysis \Hy*drol"y*sis\, n. [Hydro-, 1 + -lysis.] (Chem.)
   A chemical process causing the splitting of a chemical bond
   by the addition of the elements of water. Where the bond
   which is split is not part of a ring structure, this process
   causes formation of two compounds from one compound plus
   water, as in the hydrolysis of the ester bonds of fats during
   saponification.
   [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

hydrolysis
    n 1: a chemical reaction in which water reacts with a compound
         to produce other compounds; involves the splitting of a
         bond and the addition of the hydrogen cation and the
         hydroxide anion from the water