word-forming element usually meaning "with, together," from Latin com, archaic form of classical Latin cum "together, together with, in combination," from PIE *kom- "beside, near, by, with" (compare Old English ge-, German ge-). The prefix in Latin sometimes was used as an intensive.

Before vowels and aspirates, it is reduced to co-; before -g-, it is assimilated to cog- or con-; before -l-, assimilated to col-; before -r-, assimilated to cor-; before -c-, -d-, -j-, -n-, -q-, -s-, -t-, and -v-, it is assimilated to con-, which was so frequent that it often was used as the normal form.

also *ghed-, Proto-Indo-European root meaning "to seize, to take." 

It might form all or part of: apprehend; apprentice; apprise; beget; comprehend; comprehension; comprehensive; comprise; depredate; depredation; emprise; enterprise; entrepreneur; forget; get; guess; impresario; misprision; osprey; predatory; pregnable; prehensile; prehension; prey; prison; prize (n.2) "something taken by force;" pry (v.2) "raise by force;" reprehend; reprieve; reprisal; reprise; spree; surprise.

It might also be the source of: Greek khandanein "to hold, contain;" Lithuanian godėtis "be eager;" second element in Latin prehendere "to grasp, seize;" Welsh gannu "to hold, contain;" Russian za-gadka "riddle;" Old Norse geta "to obtain, reach; to be able to; to beget; to learn; to be pleased with;" Albanian gjen "to find."

word-forming element meaning "before," from Old French pre- and Medieval Latin pre-, both from Latin prae (adverb and preposition) "before in time or place," from PIE *peri- (source also of Oscan prai, Umbrian pre, Sanskrit pare "thereupon," Greek parai "at," Gaulish are- "at, before," Lithuanian prie "at," Old Church Slavonic pri "at," Gothic faura, Old English fore "before"), extended form of root *per- (1) "forward," hence "beyond, in front of, before."

The Latin word was active in forming verbs. Also see prae-. Sometimes in Middle English muddled with words in pro- or per-.