The Collaborative International Dictionary of English v.0.48:

Saponify \Sa*pon"i*fy\, v. t. [imp. & p. p. Saponified; p. pr.
   & vb. n. Saponifying.] [L. sapo, -onis, soap + -fy: cf. F.
   saponifier.]
   To convert into soap, as tallow or any fat; hence (Chem.), to
   subject to any similar process, as that which ethereal salts
   undergo in decomposition; as, to saponify ethyl acetate.
   [1913 Webster]

WordNet (r) 3.0 (2006):

saponify
    v 1: become converted into soap by being hydrolized into an acid
         and alcohol as a result of being treated with an alkali;
         "the oil saponified"
    2: convert into soap by hydrolizing an ester into an acid and
       alcohol as a result of treating it with an alkali; "saponify
       oils and fats"