libertarian Syllabification: (lib·er·tar·i·an)Pronunciation: /ˌlibərˈte(ə)rēən/Translate libertarian | into Italian Definition of libertarian noun 1an adherent of libertarianism: [as modifier]:libertarian philosophy a person who advocates civil liberty. 2 Philosophy a person who believes in the doctrine of free will. Origin: late 18th century (sense 2): from liberty, on the pattern of words such as unitarianlibertarian in other Oxford dictionaries Definition of libertarian in the British & World English dictionary