The Collaborative International Dictionary of English v.0.48:

Privet \Priv"et\, n. [Cf. Scot. privie, Prov. E. prim-print,
   primwort. Prob. for primet, and perh. named from being cut
   and trimmed. See, Prim, a., and cf. Prime to prune,
   Prim, n., Prie, n.] (Bot.)
   An ornamental European shrub (Ligustrum vulgare), much used
   in hedges; -- called also prim.
   [1913 Webster]

   Egyptian privet. See Lawsonia.

   Evergreen privet, a plant of the genus Rhamnus. See
      Alatern.

   Mock privet, any one of several evergreen shrubs of the
      genus Phillyrea. They are from the Mediterranean region,
      and have been much cultivated for hedges and for
      fancifully clipped shrubberies.
      [1913 Webster]

WordNet (r) 3.0 (2006):

privet
    n 1: any of various Old World shrubs having smooth entire leaves
         and terminal panicles of small white flowers followed by
         small black berries; many used for hedges