(politics) A member of a political party or movement that uses the term "Libertarian" in its name (e.g., the Libertarian Party of the United States); one who is likely to support policies that are libertarian.

(politics) Of, or pertaining to, a Libertarian Party.

One who advocates liberty, either generally or in relation to a specific issue.

(chiefly US) A believer in right-libertarianism, a political doctrine that emphasizes individual liberty and a lack of governmental regulation, intervention, and oversight both in matters of the economy (‘free market’) and in personal behavior where no one’s rights are being violated or threatened.

(chiefly UK, Ireland) A left-libertarian, an antiauthoritarian believer in both individual freedom and social justice (social equality and mutual aid).

(philosophy) A believer in the freedom of thinking beings to choose their own destiny, i.e. a believer in free will as opposed to those who believe the future is predetermined.

Having the beliefs of libertarians; having a relative tendency towards liberty.