Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
immūgio (inm-), īvi or ĭi, 4, v. n. [inmugio], to bellow, roar, or resound in or at (poet.): curvisque immugiit Aetna cavernis, Verg. A. 3, 674: procella Antennae immugit, Sil. 17, 257: maestoque immugit regia luctu, Verg. A. 11, 38: judicaturo Domino lugubre mundus immugiet, Hier. Ep. 14.