Entry 2 senses · 2 variants Webster, 1913 Libertarian /(-tā"rĭ*an)/ · Lib·er·ta·ri·an · IPA /ˌlɪb.əɹˈtɛ.ɹi.ən/ a. n. 01 a. Pertaining to liberty, or to the doctrine of free will, as opposed to the doctrine of necessity. 1. Pertaining to liberty, or to the doctrine of free will, as opposed to the doctrine of necessity. 02 n. One who holds to the doctrine of free will. 1. One who holds to the doctrine of free will.