Entry 1 sense Webster, 1913 Radiolarian /(rā`dĭ*ō̇*lā"rĭ*an)/ · Ra·di·o·la·ri·an · IPA /ˌɹeɪ.di.oʊˈlɛɹi.ən/ 01 a. Of or pertaining to the Radiolaria. 1. Of or pertaining to the Radiolaria.(Zool.)