plutonic Syllabification: (plu·ton·ic)Pronunciation: /plo͞oˈtänik/Definition of plutonic adjective 1 Geology relating to or denoting igneous rock formed by solidification at considerable depth beneath the earth’s surface. 2 (Plutonic) relating to the underworld or the god Pluto. plutonic in other Oxford dictionaries Definition of plutonic in the British & World English dictionary