A libertine [from the Latin word for "free"] is a free-thinker, especially in religious (which these days means "cultural") matters, and struggles to free himself from the restraints of all prevailing conventions. Because such free thought must be suppressed, "libertine" has come to be a synonym for "leading a dissolute life"; relatively few libertines, however, do. See: KICK BACK.
The Marquis de Sade freely admitted to being a libertine. The origin of the word is the Latin for 'freed man', but it is used to mean a person who behaves immorally – especially in sexual matters. (See also Sadism.)
Libertine has come to mean one devoid of any restraints, especially one who ignores or even spurns religious norms, accepted morals, and forms of behavior sanctioned by the larger society. The philosophy gained new-found adherents in the 18th and 19th centuries, particularly in France and Britain. Notable among these were John Wilmot, 2nd Earl of Rochester, the Marquis de Sade, and Aleister Crowley.