libertarian

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who advocates maximizing individual rights and minimizing the role of the state.
• noun One who believes in free will.

from The Century Dictionary.

• Of or pertaining to liberty, or to the doctrine of the freedom of the will (especially in an extreme form), as opposed to the doctrine of necessity; advocating the doctrine of free will: opposed to necessitarian.
• noun One who maintains the doctrine of the freedom of the will (especially in an extreme form): opposed to necessitarian.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Pertaining to liberty, or to the doctrine of free will, as opposed to the doctrine of necessity.
• noun One who holds to the doctrine of free will.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One who advocates liberty either generally or on a specific issue, e.g. "civil libertarian" (in favour of civil liberties).
• noun A believer in a political doctrine that emphasizes individual liberty and a lack of governmental regulation and oversight both in matters of the economy ('free market') and in personal behavior where no one's rights are being violated or threatened. Also 'classical liberal', akin to 'anarcho-capitalist'.
• noun An anarchist, typically with socialist implications.
• noun philosophy A believer in thinking beings' freedom to choose their own destiny, i.e. a believer in free will as opposed to those who believe the future is predetermined.
• noun US, prefixed to "Republican" a member of the Republican Party (especially a legislator) who emphasizes economic and Constitutional, rather than religious and personal, aspects of the party's platform.
• adjective Having the beliefs of libertarians; a relative tendency towards liberty.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an advocate of libertarianism
• noun someone who believes the doctrine of free will