The Collaborative International Dictionary of English v.0.48:

Apportion \Ap*por"tion\, v. t. [imp. & p. p. Apportioned; p.
   pr. & vb. n. Apportioning.] [OF. apportionner, LL.
   apportionare, fr. L. ad + portio. See Portion.]
   To divide and assign in just proportion; to divide and
   distribute proportionally; to portion out; to allot; as, to
   apportion undivided rights; to apportion time among various
   employments.
   [1913 Webster]

WordNet (r) 3.0 (2006):

apportion
    v 1: distribute according to a plan or set apart for a special
         purpose; "I am allocating a loaf of bread to everyone on a
         daily basis"; "I'm allocating the rations for the camping
         trip" [syn: allocate, apportion]
    2: give out as one's portion or share [syn: share, divvy up,
       portion out, apportion, deal]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "apportion":
   accord, align, allocate, allot, array, assign, award,
   be partners in, bestow, carve, carve up, collocate, compose,
   cooperate, count, cut, cut up, deal, deal out, decrease, dish out,
   dispense, dispose, distribute, district, divide,
   divide into shares, divide up, divide with, divvy, divvy up,
   divvy up with, dole out, fix, give, go even stephen,
   go fifty-fifty, go halvers, go halves, go shares, grant, halve,
   increase, line, line up, lot, marshal, measure, mete out, number,
   parcel, parcel out, part, partition, place, portion, portion out,
   present, prorate, quantify, quantize, quota, rally, range, rate,
   ration, reduce, regiment, section, segment, separate, serve,
   set out, share, share in, share out, share with, shift, slice,
   slice the pie, slice up, space, split, split the difference,
   split up, subdivide, zone