Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
fornĭcātus, a, um, adj. [fornix, I.], vaulted, arched.
fornĭcor, ātus, 1, v. dep. n. [id. II.], to commit whoredom or fornication (eccl. Lat.), Tert. Pudic. 22; Vulg. Gen. 38, 24 et saep.