The Collaborative International Dictionary of English v.0.48:

Expurgation \Ex`pur*ga"tion\, n. [L. expurgatio justification,
   excuse: cf. F. expurgation.]
   The act of expurgating, purging, or cleansing; purification
   from anything noxious, offensive, sinful, or erroneous.
   --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

expurgation
    n 1: the deletion of objectionable parts from a literary work
         [syn: expurgation, castration]