Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
irrĕmissĭbĭlis (inr-), e, adj. [2. inremissibilis], unpardonable, irremissible (eccl. Lat.): peccata, Tert. Pudic. 2: blasphemia, Hier. Ep. 42, 1.