The Collaborative International Dictionary of English v.0.48:

Nolle prosequi \Nol"le pros"e*qui\ [L., to be unwilling to
   prosecute.] (Law)
   Will not prosecute; -- an entry on the record, denoting that
   a plaintiff discontinues his suit, or the attorney for the
   public a prosecution; either wholly, or as to some count, or
   as to some of several defendants.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nolle prosequi
    n 1: an entry in the court record to the effect that the
         plaintiff or prosecutor will not proceed [syn: nolle
         prosequi, nol pros]
    v 1: drop prosecution of by entering a nolle prosequi in the
         court records; "They nolle prossed the charge" [syn: nolle
         pros, nolle prosequi, nol.pros.]