xenolithEnglishOxford Dictionary of Englishxenolith /ˈzɛnə(ʊ)lɪθ / ▸ noun Geology a piece of rock within an igneous mass which is not derived from the original magma but has been introduced from elsewhere, especially the surrounding country rock. – DERIVATIVES xenolithic /ˌzɛnə(ʊ)ˈlɪθɪk / adjective