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. [1913 Webster]

pro-, prefix.
1 favouring or supporting (pro-government).
2 acting as a substitute or deputy for (proconsul).
3 forwards (produce).
4 forwards and downwards (prostrate).
5 onwards (proceed; progress).
6 in front of (protect).

pro-, prefix before in time, place, order, etc. (problem; proboscis; prophet).

Etymology:
Gk pro before