Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
permĭtĭālis, e, adj. [permities], fatal, destructive, ruinous: id quod nusquam sine permitiali Discidio potis est sejungi, Lucr. 1, 451 Munro (Lachm. perniciali).