Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. fornĭcātĭo, ōnis, f. [fornicatus], a vaulting or arching over, a vault, arch (post-Aug.): parietum, Vitr. 6, 11: lapidum, Sen. Ep. 95, 53.
2. fornĭcātĭo, ōnis, f. [fornicor], whoredom, fornication (eccl. Lat.), Tert. Pudic. 1; 2; 16; 22; Vulg. Num. 14, 33 al.