Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sĕquestrārĭus, a, um, adj. [sequester, I.], of or belonging to sequestration: actio, i. e. in which the thing contested is deposited in the hands of a third party, Dig. 16, 3, 12; 4, 3, 9.