Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
* rĕbellĭum, ii, n. [rebello], a renewal of war, revolt, rebellion (a collat. form for rebellio, like consortium for consortio, contagium for contagio, etc.): qui pacatos ad rebellium incitasset, Liv. 42, 21, 3 Gronov. (dub.; Weissenb. rebellandum).