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]