The Collaborative International Dictionary of English v.0.48:

Privateer \Pri`va*teer"\ (pr[imac]`v[.a]*t[=e]r"), n. [From
   Private.]
   1. An armed private vessel which bears the commission of the
      sovereign power to cruise against the enemy. See Letters
      of marque, under Marque.
      [1913 Webster]

   2. The commander of a privateer.
      [1913 Webster]

            Kidd soon threw off the character of a privateer and
            became a pirate.                      --Macaulay.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Privateer \Pri`va*teer"\, v. i. [imp. & p. p. Privateered
   (pr[imac]`v[.a]*t[=e]rd"); p. pr. & vb. n. Privateering.]
   To cruise in a privateer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

privateer
    n 1: an officer or crew member of a privateer [syn: privateer,
         privateersman]
    2: a privately owned warship commissioned to prey on the
       commercial shipping or warships of an enemy nation