The Collaborative International Dictionary of English v.0.48:

Apportionment \Ap*por"tion*ment\, n. [Cf. F. apportionnement,
   LL. apportionamentum.]
   The act of apportioning; a dividing into just proportions or
   shares; a division or shares; a division and assignment, to
   each proprietor, of his just portion of an undivided right or
   property. --A. Hamilton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

apportionment
    n 1: the act of distributing by allotting or apportioning;
         distribution according to a plan; "the apportionment of
         seats in the House of Representatives is based on the
         relative population of each state" [syn: allotment,
         apportionment, apportioning, allocation, parceling,
         parcelling, assignation]