Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
offusco (obf-), āre, v. a. [ob-fusco], to darken, obscure; only trop., to vilify, degrade (eccl. Lat.): justitiam, Tert. adv. Marc. 2, 12: aliquem, id. Spect. 22: quoniam offuscata sum, Ambros. in Psa. 118, Serm. 2, § 9.