Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
subsortītĭo, ōnis, f. [subsortior], a choosing of substitutes by lot, sc. of other judges in place of those rejected by the parties, Cic. Verr. 2, 1, 61, § 157; id. Clu. 33, 91; a selection of citizens to receive corn in place of those who had died: subsortitio a praetore fieret, Suet. Caes. 41 fin.