The Collaborative International Dictionary of English v.0.48:

Reapportionment \Re`ap*por"tion*ment\ (-ment), n.
   A second or a new apportionment.
   [1913 Webster]

WordNet (r) 3.0 (2006):

reapportionment
    n 1: a new apportionment (especially a new apportionment of
         congressional seats in the United States on the basis of
         census results) [syn: reallotment, reapportionment,
         reallocation]