Source : Webster's Revised Unabridged Dictionary (1913)

Pro- \Pro-\ [L. pro, or Gr. ?. See {Pro}.]
   A prefix signifying before, in front, forth, for, in behalf
   of, in place of, according to; as, propose, to place before;
   proceed, to go before or forward; project, to throw forward;
   prologue, part spoken before (the main piece); propel,
   prognathous; provide, to look out for; pronoun, a word
   instead of a noun; proconsul, a person acting in place of a
   consul; proportion, arrangement according to parts.