The Collaborative International Dictionary of English v.0.48:

Pre- \Pre-\ [L. prae, adv. & prep., before, akin to pro, and to
   E. for, prep.: cf. F. pr['e]-. See Pro-, and cf. Prior.]
   A prefix denoting priority (of time, place, or rank); as,
   precede, to go before; precursor, a forerunner; prefix, to
   fix or place before; pre["e]minent eminent before or above
   others. Pre- is sometimes used intensively, as in prepotent,
   very potent. [Written also pr[ae]-.]
   [1913 Webster]