Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
2. incestus, ūs, m. [1. incestus, II.], unchastity, incest (mostly Ciceron.): quaestio de incestu, Cic. Mil. 22, 59; id. Brut. 32, 122; 124; id. N. D. 3, 30, 74 Klotz; Liv. 4, 44 Weissenb.; Val. Max. 6, 3, 7.