1. A freedman; one freed from slavery. [Roman]
2a. The name given to certain "free-thinking" sects (of France and elsewhere on the continent) of the sixteenth century.
2b. One who holds free or loose opinions about religion; a free-thinker.
2c. One who follows his own inclinations or goes his own way; one who is not restricted or confined.
3. A man who is not restrained by moral law, especially in his relations with the female sex; one who leads a dissolute, licentious life.
The word 'libertine' was first applied in the 1550s to a sect of Protestants in northern Europe who, with unimpeachable logic, reasoned that since God had ordained all things, nothing could be sinful. They proceeded to act accordingly. Their views were regarded with horror by both Catholics on one side and Calvinists on the other.
[AC Grayling, The Form of Things]