The Collaborative International Dictionary of English v.0.48:

Libertine \Lib"er*tine\ (-t[i^]n), n. [L. libertinus freedman,
   from libertus one made free, fr. liber free: cf. F. libertin.
   See Liberal.]
   1. (Rom. Antiq.) A manumitted slave; a freedman; also, the
      son of a freedman.
      [1913 Webster]

   2. (Eccl. Hist.) One of a sect of Anabaptists, in the
      fifteenth and early part of the sixteenth century, who
      rejected many of the customs and decencies of life, and
      advocated a community of goods and of women.
      [1913 Webster]

   3. One free from restraint; one who acts according to his
      impulses and desires; now, specifically, one who gives
      rein to lust; a rake; a debauchee.
      [1913 Webster]

            Like a puffed and reckless libertine,
            Himself the primrose path of dalliance treads.
                                                  --Shak.
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   4. A defamatory name for a freethinker. [Obsolescent]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Libertine \Lib"er*tine\, a. [L. libertinus of a freedman: cf. F.
   libertin. See Libertine, n. ]
   1. Free from restraint; uncontrolled. [Obs.]
      [1913 Webster]

            You are too much libertine.           --Beau. & Fl.
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   2. Dissolute; licentious; profligate; loose in morals; as,
      libertine principles or manners. --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

libertine
    adj 1: unrestrained by convention or morality; "Congreve draws a
           debauched aristocratic society"; "deplorably dissipated
           and degraded"; "riotous living"; "fast women" [syn:
           debauched, degenerate, degraded, dissipated,
           dissolute, libertine, profligate, riotous,
           fast]
    n 1: a dissolute person; usually a man who is morally
         unrestrained [syn: libertine, debauchee, rounder]