The Collaborative International Dictionary of English v.0.48:

Pro \Pro\, adv.
   For, on, or in behalf of, the affirmative side; -- in
   contrast with con.
   [1913 Webster]

   Pro and con, for and against, on the affirmative and on the
      negative side; as, they debated the question pro and con;
      -- formerly used also as a verb.

   Pros and cons, the arguments or reasons on either side.
      [1913 Webster]