The Collaborative International Dictionary of English v.0.48:

Libertinism \Lib"er*tin*ism\ (-t[i^]n*[i^]z'm), n.
   1. The state of a libertine or freedman. [R.] --Hammond.
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   2. Licentious conduct; debauchery; lewdness.
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   3. Licentiousness of principle or opinion.
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            That spirit of religion and seriousness vanished all
            at once, and a spirit of liberty and libertinism, of
            infidelity and profaneness, started up in the room
            of it.                                --Atterbury.
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Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "libertinism":
   broad-mindedness, debauchery, debauchment, dissipation,
   dissoluteness, fastness, free thought, freethinking, gallantry,
   latitudinarianism, liberalism, liberation, libertarianism,
   libertinage, license, licentiousness, open-mindedness, profligacy,
   rakishness, tolerance, toleration, unbigotedness, unbridledness,
   venery, wenching, whoring, wildness