Favour or support; forwards, out, or away; substitute or deputy.
[Latin pro, forward, in front of, on behalf of, instead of, on account of.]
Modern examples in which it has the sense of favouring or supporting include pro-choice, advocating the legal right of a woman to choose whether or not she will have an abortion; pro-European, favouring or supporting closer links with the European Union.
Words in which it has a sense of motion forwards, out, or away include proceed (Latin procedere, from cedere, go); propel (Latin propellere, from pellere, to drive); and prostrate (Latin prostratus, thrown down, from sternere, lay flat).
In a few words it has the sense of something acting as a substitute or deputy: proconsul (Latin pro consule, (one acting) for the consul), a governor of a province in ancient Rome, having much of the authority of a consul; pro-vice-chancellor, an assistant or deputy vice-chancellor of a university; procaine, a synthetic compound used as a local anaesthetic, especially in dentistry, named because it was a substitute for cocaine.
Other examples imported from Latin include profane (Latin profanus, outside the temple, not sacred, from fanum, temple); prohibit (Latin prohibere, keep in check, from habere, to hold); promise (Latin promittere, put forth, promise, from mittere, send); prospect (Latin prospicere, look forward, from specere, to look); and proverb (Latin proverbium, from verbum, word).
See also pur-.