The Collaborative International Dictionary of English v.0.48:

Pro \Pro\, prep. [L.; akin to prae before, Gr. ?, and E. for.
   See For, prep., and cf. Prior, a.]
   A Latin preposition signifying for, before, forth.
   [1913 Webster]

   Pro confesso [L.] (Law), taken as confessed. The action of
      a court of equity on that portion of the pleading in a
      particular case which the pleading on the other side does
      not deny.

   Pro rata. [L. See Prorate.] In proportion; proportion.

   Pro re nata [L.] (Law), for the existing occasion; as
      matters are.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pro rata \Pro` ra"ta\ [L.]
   In proportion; proportionately; according to the share,
   interest, or liability of each.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pro rata
    adv 1: in proportion [syn: proportionately, pro rata]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "pro rata":
   ad valorem, appraised, assessed, distributional, distributive,
   distributively, each to each, equal, evaluated, even stephen,
   fifty-fifty, good for, half, half-and-half, halvers,
   in equal shares, in proportion, particular, per capita, per head,
   priced, prized, proportional, proportionate, proportionately,
   prorated, rated, respective, respectively, several, severally,
   valued, valued at, worth



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PRO RATA. According to the rate, proportion or allowance. A creditor of an
insolvent estate, is to be paid pro rata with creditors of the same class.