Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
in-concessus, a, um, adj., not allowed, impossible (not ante-Aug. and rare): hymenaei, unlawful, forbidden, Verg. A. 1, 651; cf. ignes, Ov. M. 10, 153: spes, id. ib. 9, 638: cum totum exprimere paene sit homini inconcessum, Quint. 10, 2, 26.