Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
illēgĭtĭmus (inl-), a, um, unlawful, not permitted, Paul. Sent. 5, 4, 15.
Adv.: illēgĭtĭmē, unlawfully, illegitimately: qui concipiuntur, Gai. Inst. 1, § 89.